The life and times of Kibutsuji Muzan, bored immortal guy
by Revantio
Summary: Sometimes he wanted to apologize to the Ubuyashikis because their curse came from him. Cursed for generations and generations until he died. Tough luck cousins, he doesn't know if he could die either. They can suffer together from afar, in family spirits and all. / In which Muzan is a decent guy all along, and canon somehow still found its way.
1. Chapter 1

If anyone ever asked about his sickly condition, Kibutsuji Muzan would reply with a simple shrug, then dive in to read his book, refusing to answer.

For you see, at the tender age of 15 years old, Kibutsuji Muzan has _Existential Crisis_.

Honestly, he is glad he is sick. As those few noble families lucky enough to be educated, Muzan knew nothing but War awaits outside. Had he been healthy, he would have been sent to another province for any clan in favor of Kibutsujis right now, be it Minamoto, Sakamoto, or whatever, fighting their wars. It was early death all the same.

On his sick bed however, he could enjoy the tranquility of the sun while he drowned his mind in books; poisons, language of flowers, tales of myths. And every time his curiosity would be satisfied as it grows. He could demand more information normally would not be available for other teenage boys of his age. And he is happy with it, for he could set a slight puppy eyes and say, '_guess i'd _die_ with my curiosity_' and his fool of a family would get whatever scroll it is he wanted. Easy.

But therefore lies the problem.

Kibutsuji Muzan was a curious being. Had he not been sickly, maybe he could wring his way out of battle to be a scholar. Traveling around Japan, reading, studying, researching.. That would be heaven. All those knowledge he could dig out of the dark...

Plus, he thinks tiredly, being sick is not fun. He feels tired all the time. His could feel his every bones ache with every minute twitch, he wanted to scream and cry but he is too tired to do anything. But then again, he doesn't want to be healthy either; not out to those stupid wars. And since he is destined to rot away here all alone, it would be nice if he could die quickly instead. But, he thinks again, rather than battlefield, he prefers dying sickly like this, surrounded by his books.

But again, being sick is not fun, but healthy only leads to grown up children with knives and—

Again, Kibutsuji Muzan, 15 years old, has _Existential Crisis_.

* * *

His family loves him, he knew.

His family is trying their best to cure him, they never gave up, no matter how fruitless it is, he knew.

And those are the only reason Muzan forced himself to be obedient to this Doctor. How did his family managed to find a super sketchy one, he thinks, is beyond him. But his older sister and mother, who always back him up in his bed-ridden books scavenger, are the one who recommends him.

So, pulling his scowl back and forcing his skin to stop crawling in disgust at the sight of that very suspicious smile, Muzan gave the Doctor his noble, polite, yet obviously _fuck-off _smile. Sure, he'd drink his medicine. Sure, he'd be polite and behave (he scoffed at this, as if he doesn't know his manners, _please_) in front of this pervert, but only because his mother and older sister insists.

It doesn't help that the medicine smell and tastes disgusting, _what the hell_.

Muzan sighed, putting his glass of water down and laying down on his futon; face scrucnhing up and trying not to vomit. The things he do for love.

* * *

Muzan was cured.

It was a miracle. Just as that sketchy Doctor miraculously disappeared.

When he tried to step out to his garden on the morning spring however, his skin _burned_ from sunlight. And almost instantly they _vaporized_. His scream was apparently agonized enough his mother ordered to find that Doctor and make him pay.

They never find him however. Not even a trace of him. He disappeared to thin air.

_Fucking asshole_, he hissed under his breath, glaring to the afternoon sun. What good is he healed if he can't even travel like a normal person?

* * *

Sometimes, his home smells of blood.

His brothers, returning from war, did not return in pristine condition. It was normal, he had used to the smell of blood since his father and grandfather returned with blood soaking their clothes. What he did not expect however, how his hunger abruptly intensified. Sure, he has always been hungry since he was healed and banished from the sun, but it was sated bit by bit with strictly red meat diet, half cooked as it was. He had bulshitted that it was one of the last thing that asshole doctor prescribed to him, and apparently his family has no business not trusting their sickly son.

But smelling the coppery tang of human blood, he so very badly wanted to take a bite off of his brother's shoulder. He is muscled well, so it should be very chewy, his meat, and fresh, and juicy too. Or he could take his hand and picked his skin apart from his fingers. He could bite them off slowly but surely, an endless satisfaction as blood flows to his mouth—

_What the fuck_?

Muzan whirled around, punching the wall to quell his creepy thoughts which had come out of nowhere.

_What The Fuck_?

... His fist was _burrowed_ in the stone wall, spider-web cracks crawling from the hole he just—just _punched through_.

Suddenly, he was more aware of footsteps coming his way than his bleeding fist and elongated nails, and in a fit of panic, he ran. The night covered his figure as he easily jumped through stone wall and jumped over rooftops (_WHAT THE FUCK_?) in such impossible speed and feats no human capable of, without sound whatsover, _no problem_, to the streets.

* * *

After saving one of his gardener from being raped in the streets by biting the neck of the man off, and subsequently made her scream in terror, Muzan sat down. Alone on the corner of the streets, his face a perfect mask of calm.

_He is an asshole_, Muzan thinks, looking at the corpse of the man with blood leaking out freely from where he chewed his neck. And Ayame-san was an excellent gardener. As if a Young Master like him would let his subjects in danger. Also, his meat vaguely taste like grilled chicken but chewy like red meat. He wonders if other human meat also taste like chicken. Or maybe he's finally losing his mind, who knows, right?

...

_FUCK_.

...

That fucking Piece of Shit Doctor has turned him into a Vampire. Or Ghoul. Or other similar creature.

_What manner of bullshit is this_?

He knows his shit, he had suspected since he couldn't get out of the sun. But he could maintain human diet just fine, and he thought—he thought—

A low, feral growl tore the calm night. It came from him, he realized.

He had killed someone. It was easy, his nails tore the man's chest like paper. His mouth, his fangs, bite the chunk of meat off the man's neck like any other food. _He had killed someone_. He needed human meat to survive.

He would be discovered by patrols, Muzan thinks, locating said patrol some hundreds of meters from his location just fine. His senses are sharp, too sharp for a human; he could see clearly even in the dark, could hear rats moving around and down the sewer, and could smell blood and fresh corpse in front of him with such sweetness it made him want to puke but also want to lick it clean.

(His family couldn't live with him like this, he thinks, they would find the corpse and his trail. He couldn't live with coppery tang around the house for days, he'd go _mad_ for sure. He'd attack his family in no time. Holding back this hunger and bloodlust has been hard enough all this time, he did not need any bait.

He had to leave. Muzan doesn't exactly want to, considering his family but—_he had to_.)

Steeling his resolve, Muzan jumped over another rooftop and ran.

"I'm going to find you," he promised, hissed lowly; red slitted eyes glinting in the dark, "you will fucking _pay_."

* * *

Living on the streets has been... illuminating, to say the least.

Apparently he couldn't get poisoned. Poison ivy had no effect to him, nor any other poisonous berries he chewed on (and fully expected to die). Or sick, as he had not sleep and simply sit under a waterfall when he sulked on his condition for days. He could also glare a bear away apparently, if he growled hard enough. Falling down from a cliff and smushing his head is also fine, he could grow his organs back in like, a minute. His twisted ankle would right itself in seconds. Starving himself only leads to an unconscious rage and he had come to consciousness with a corpse of another poor sod, gnawing at his hand.

So. He's essentially immortal now.

Nice.

He could go incognito and travel anywhere spreading murder while researching and dig a lot of things. Whatever he wants, easy, no problem. He can even sneak in and stay at local Library if he wanted to.

Very nice.

(He pointedly doesn't think how he will probably outlive his family, or be bored for eternity, or forever unable to attend _hanabi_ in the afternoon spring. Alone walking on this stupid earth with stupid humans forever. If he does, it makes him want to _scream_.)

It also illuminates his limits on this body; or lack thereof. His steps are light and without sound even when he did not try; he had sneaked to whoever house at night, take some clothes, and get away just fine.

Among his other... crimes, however, killing gets easier.

Humans are assholes by default, himself included. So what if he jumped down on a bandit and chew his hand off? So what if he cut their limbs with his nails and easily keep them for later? So what if those assholes probably has families? He doesn't care, for sure. And if he got fighting experience from them, that's all the better.

(If you don't get the memo, he does care. Sometimes.)

* * *

In a twist of his clumsiness during battle, he found out that, by giving his blood, he could turn other humans to demons.

The soldier who raided a Raijin Temple bite his hand and promptly convulsed. Muzan slapped his head away until it twisted but, the man hadn't died. He himself had jumped up to the ceiling, standing on the supporting wood and watched as the man grew horns and fangs, twisted his neck back in place—and proceeds to murder all his comrades in a very gruesome, messy slaughter. He had been reluctant to jump down; after he perfected the art of killing while keeping himself pristine, he refused to step on such mess. But the newly-made demon had then looked at him and knelt, head bowed down in a sign of complete loyalty.

Muzan blinked.

So. He could make armies with his blood now.

Hm.

_Hmmmmm_.

Gently stepping down, he ordered the newly-made demon to be off, do whatever, stay out of trouble. And then he had disappeared, mind working on plans and hypothesis. He needs more research.

* * *

And what better place than to do research than in Hospital?

If his blood can heal twisting neck, it could probably heal other diseases too. It's high time he does something good for humanity, he thinks. Muzan easily sneaked to quarantined wing of a hospital, entering a room from the window. Experimenting, he gave the first person on the row one drip of blood, the next two drip, the next one third, and promptly disappointed when the fifth one exploded and the fourth one screamed before her feet exploded and she, too, died.

The first and second one convulsed, just like that soldier demon, and their sickly, thin body filled in easily to healthy and muscled being. Hearing footsteps, Muzan retreated to a corner, hidden by curtain. Curious on his experiments.

Nurses and a doctor filled in. His two newly made demons devoured the humans, unsurprisingly. He frowned though; they don't show the same intelligent the soldier demon has, he mused. Why is that? Stepping out of his hidden place, one of his newly made demon quiver in fear. Another one, Dumbass, he dubbed in his mind, tried to attack him. He cut Dumbass's limb off, but he still continued, and thus he punched a hole though his chest. Dumbass still moved, Muzan is slightly impressed. Scowling, Muzan decapitated him, and he finally dropped like a ragdoll.

Licking blood off his fingers for show, he glanced to the other demon.

"Begone." He said, voice cold and pissed as he had to dirty his hand, no matter how happy he is on how resilient his creation (and probably himself) is.

She 'eep'ed, before bowing down with a quivered, "Y-yes My Lord!" Before she ran off.

Muzan snorted.

This night was, at least, educational.

* * *

With such resilient soldiers, to be the _shogun_ or to not be the _shogun_, that is the question.

...

Who is he kidding? Who the hell wants to deal with imbeciles and human stupidity feat paperworks on daily basis? Not him, thank you.

* * *

Maybe his approach was wrong on this. Maybe they need... education?

Murdering a lone doctor who experimented on children, Muzan took the man's identity easily. Willing his face and body to shape like the man, he moved. With him not needing much sleep, he could brainstorm medical knowledge needed for a doctor in a week. In his study, he almost forget his purposes on studying this feverishly. Almost.

He attended houses. Offering his help to those with 'Incurable' label on their profile. Muzan is in his Doctor's shoes now, offering shady treatment, charming his way to families. However disgusting this is, he had to. _For science_.

Muzan asked for a night to heal this family's sickly son; a night for the family to be off from their house except their sickly member. With a drop of his blood he turned their son to a demon. With his chilly voice and hands which digs to the new demon's shoulder, he explained his circumstances, his name, how he has parents and _blabla_ about his life. Muzan also explained to the parents that he needs strictly red meat diet, not to be let out on sunlight, and introducing their demon son to their parents.

The family thanked him feverishly. And they seemed fine, after that.

Until two weeks later that demon son went rogue and killed his entire family.

Muzan scowled.

He tried four more times, because one data is not objective enough. And between one to four weeks, all four results are the same with his first experiment. Family slaughter.

Muzan scowled harder.

_Well_, a laugh which suspiciously sounds like his mother rings in his head, every time he did something which is apparently stupid for her, _at least you tried!_

* * *

Life gets boring after some decades.

Muzan learned a lot of things about the world and about himself. His presence has become a myth, his name whispered in fear. A decade ago, he had found a cult worshipping demon and promptly appeared in one of their creepy ceremony. He turned the leader to a mindless demon, and watched he slaughtered his cult members with his Blood Demon Art. Serves them right, creepy assholes. That was probably when he had become (in)famous, as he had introduced himself then.

His scattering demons reports to him time to time, as he discovered they could communicate through telepathy. They brought him news, rumours, development on their powers (they grew more powerful with each human they eat, apparently), and such. Things to confirm his suspicions on political climate and other things.

In his long life, he had shape-shifted to a lot of people, had studied medicine, architecture, art, history, mythology, and worked on a lot of projects at once. It was during this time he discovered he could make organs in himself; more brains, more hearts, more kidneys to drink himself stupid. He made educational books, and debate on his knowledge with other scientists, under several wonderful years.

True, sometimes people who knew who he truly is (usually cult members) asked for immortality and such from him. And depending on how much of an asshole they are, he either exploded them on sight, made them dinner, or watch them convulse and survive. From time to time, families of those people hunt him down and tried to kill him; they rarely succeeded, or if they do, their _katana_ can't kill him, and he got to watch them gawk as his limbs grew on remarkable speed.

Life gets boring when knowledge stops sparking his curiosity, and he retreated in a small estate under the woods. It was owned by a couple of amnesiac elders who thought of him as his lost grandson when he wandered there. They still count him as his grandson even after a year later, and Muzan is content on playing grandson, mostly doing _nothing_.

The cult members still find him, probably because his demons telling his whereabouts, but he doesn't mind much. As long as he didn't dirty the tatami with blood, grandpa and grandma wouldn't yell at him.

And then a Samurai named Tsugikuni Michikatsu came at him.

* * *

Michikatsu twitched, apparently miffed at how cold Muzan's expression is. How cold and bored his red eyes are as he heard the man talk and what he wanted. Muzan smiled to grandma who served them tea though, expression broke to something warm as grandma pats his head and '_be good with the handsome guest won't you?_'

When grandma was out of earshot, he ignored how Michikatsu opened his mouth to talk, purposely sipping his tea while closing his eyes. Michikatsu twitched more.

"So," he put his tea down, voice bored, "you want to grow stronger than your twin brother?" He asked; confirmed really.

"He is a Demon Slayer." Michikatsu bit out, trying very hard to stay still.

Ah, those. The Demon Slayer Corps, an organization founded by the Ubuyashikis, his Cousin family, had appeared and apparently they are _hellbent_ on killing him, hunting his demons one by one. He had wondered about his own family, but at the time one of his demons told him his family was slaughtered by rivaling clan some twenty years ago, he had gone numb. Sometimes he wanted to apologize to his Cousin family because they are cursed _because_ of him. Cursed for generations and generations until he died.

Tough luck cousins, he doesn't know if he could die either. They can suffer together from afar, in family spirits and all.

Muzan peered to his katana, observed how the Samurai breathed, and snorted. "What betrayal," he sighed, mockingly dramatic, "a demon slayer asking to be demon, what tragedy."

Michikatsu was very, very still. Trying very, very hard not to scowl because of course he values his life in front of Muzan.

Muzan tried hard not to snort again. Riling him up was so fun. "Okay, Slayer." He agreed, "I will make you the strongest yet." And he will. Those who mastered Breathing Technique are stronger, they can withstand a lot of his blood. "I have but one condition."

Michikatsu waited.

Muzan smiled. It was not a nice smile.

"You have to kill me in the end."

* * *

_(He loved his studies, he really does. He loved every inventions humans made. He loved their happiness and silliness, their genuine curiosity._

_He loved human just as he loathed them._

_He loathed their greed. How he loathed their wars. How he loathed their stupidity. _

_He would look at his reflection and something tiny in his brain said, _you are monster_._

_It said, _you are a wretched creature. causing all those deaths, turning blind eye and humoring wretched ideals_._

_If he is going to hell anyways, he thinks, just do it quickly. Anyone. Just send him to hell already.)_

* * *

Michikatsu can handle a _lot_ of his blood.

Muzan had gone slowly, giving bits by bits for Michikatsu's body to get used to it. But it was clear that he is far stronger than regular Breath Users. He transformed, as per the usual. His swordsmanship has sharpened and sharpened every time they sparred. Breath of Moon is breathtaking to see and face, and Muzan found himself enjoying himself in adrenaline more often than not.

He gave a lot of blood for Michikatsu to convert whoever it is on from his own blood, in the end. It took nearly eight of his total blood.

But.

No matter how powerful Michikatsu become, he didn't manage to kill him.

Instead, Muzan discovered a whole lot new tricks he could do for himself. Apparently he can grow tentacles far easier now. Tentacles with mouths. And blades, and new hearts mid battle. Breath of Moon was amazing, but it could never slow the rate of his regeneration, which is terrifying in its own rights. Though Michikatsu's own regeneration is remarkable, it was still seconds slower than Muzan. He had been wanting to try to shapeshift to mythical creatures too, and he did so in his battle with Michikatsu. Sure, the slayer turned demon is powerful, rightfully so.

But at the end of the day, after days of battling and trying to subdue each other, Muzan was stil the winner.

"_What the fuck?_!" Hissed Muzan to the dirt, absolutely horrified as he just reviewed the battle in his mind; realized the length of what he can do, _again_. He thought he has grown out of this 'what the fuck' phase, but obviously not.

Not too far away from him, Michikatsu flipped him off, exhausted and totally mutilated.

* * *

Michikatsu was a bitter bitch in defeat.

After he was done regenerating himself, he disappeared. To God knows where. He hadn't care too much, never did track his demons when they are off on murder spree. He was a bit disappointed that he can't see his reaction on Muzan's branding of Michikatsu though; a 'tattoed' kanji of 'One' on each left side of his eyes. Muzan had given it to him because he was his first demon student, but for Michikatsu who hated defeat, it must be some kind of brand or reminder of defeat. His rage would be funny. But no matter. His demons are grown men regardless of their human age, including Michikatsu, and for Muzan it meant they handled their murder spree responsibilites on their own.

He didn't count how many years has passed after that. Eventually, grandma and grandpa died. He dig them their graves himself, left Nakime to include the house in her Interdimensional Labyrinth Blood Demon Art (because he likes her enough) to take care of it and promptly wandered off some more.

Muzan decided he wanted to update his knowledge on current science development since he had gone and rolled in university easily. A new branch of medicine, of toxins, has opened. Interested, he became close to his mentor there, a gentle woman named Tamayo. They would discuss poisons from animals and plants, break their components down, and combine them; the last one if only to humour Muzan.

Life was moving again from Muzan. It was slow, but it was enjoyable. Still with the same 'assholes demanding immortality' things, or if he's bored enough, he still came to bust Cult Gatherings to turn few of them to demons, and few of them to dinner. Demon Slayer Corps never get a hold of him and his demons are cutely loyal to him; choosing death than telling his whereabouts. Few well placed praises, head-pats, and cruel punishments do you wonders, apparently.

So he was understandably shocked when one night, coming home from library, he was assaulted by a demon slayer with blazing red blade.

"Where are your manners, Slayer?" Muzan snarled.

The long-haired man in red haori stayed silent, and continued his assault.

His cut _stings_ like no other thing he ever felt. His regeneration slowed down considerably, which baffled him and scared him a bit. The Slayer was nimble, strong, slippery, blinding, and when he he hits, he hits _hard_. It was like fighting rays of sunlight; his blade shines, he could almost see lava trailing its swings. They burn his skin, he couldn't get a hold of him, and Muzan was left snarling in burning, scorching pain in his wake.

He had wanted to die, yes, he thinks quietly, but not like this. He wanted to, at least say goodbye to Tamayo. But, he thinks again, parrying the burning blade homing for his neck with his hardened nails and replied with his dancing bladed tentacles, maybe he did not get that kind of luxury after all. After all he has done. Maybe this is his time to die. This man, this Slayer, whoever he is, has rendered his regenerative abilities, he has burned his skin and wound him like no others. He had burned his heart in a lucky stab, and he _knew_ how the man is homing for another of his hearts. Like he could see _where_ his hearts are. Not even Michikatsu was able to do that.

It's hard to shape-shifts to creatures with such wounds. Muzan pulled his bone from his mutilated right hand out, parrying his sword with his hardener bone as his hand grew. Too slow. The Slayer knew this too. In the end, Muzan slowly half-assed his efforts, tired already and wanting to die. The Slayer easily burned his remaining hearts, and Muzan barely registered the pain as he was high on adrenaline, trying to parry and regenerate as much as he can while still, hopefully, looks serious.

(_Finally someone who can kill him._

_Finally he can rest._

_Finally. He is getting too bored already. And lives vaporizes when he is bored.)_

Muzan widened his eyes when the Slayer's blade was ready to decapitate his head. His reaction time was purposely slowed just so it's enough to decapitate him while Muzan dodged half-heartedly. Muzan closed his eyes, and sighed almost in relief to his upcoming death.

...

His entire body is _burning_. His wounds are _aching_. Death isn't supposed to be like _this_.

Muzan opened his eyes, this time genuinely shocked to see the red blade has stopped to graze his neck. His red eyes met that of the Slayer's, then, still shocked.

"You're a decent human being." The Slayer said, sounding confused himself.

What.

"I don't kill decent human beings."

_What_.

The Slayer stepped back then, offering his hand for Muzan to get up.

_WHAT THE FUCK?!_

* * *

After the battle; after Muzan minutely shocked as he waited for himself to regenerate properly and the Slayer had stayed and watched, they talked.

So _this_ is Tsugikuni Yoriichi, Michikatsu's twin which he wanted to surprise. Breath of The Sun, Muzan guessed, from how his blade moved, almost a mirror to his twin but not; far more powerful and heavy than Michikatsu's swings could ever be. And it nulls his regeneration almost useless.

Annoyed, he asked, "How do you even know where i am?"

Yoriichi shrugged. His face, Muzan learned, is naturally expressionless. "A demon told me."

Red eyes squinted. His demons are awfully loyal, though. "Describe it."

"One horn. Yellow eyes. Checkered skin. Demon Blood Art of poison needles."

Muzan was quiet, reviewing his brains for memories of such demon and, after the fifth sweep of his memory, he is pretty sure, none of his demons are like that. He told as much, voice genuinely puzzled, regardless his stone cold expression. "I have no such demon."

It was Yoriichi's turn to be puzzled then, as he must sense Muzan's genuine confusion. "There are rise of demon activities this past decades."

Muzan stared blankly at Yoriichi.  
Yoriichi stared back blankly.

Muzan broke the staring contest first, holding his own grudge to grumble against his tea. Instead, he forced himself to think. He hadn't do shit for the past decade, though. It was, as Nakime put it delicately, 'his vacation, unproductive years.' Late Kikio bluntly said 'this is Muzan-sama's lazy years.' But then if not him, who—?

"Michikatsu." Muzan realized. "I was his mentor. He have almost ninth of my blood." Michikatsu is building his own army, Muzan thinks. But _why_? Does he want to take over the world or something?

Yoriichi, Muzan realized, looks pinched. For any other people he was still the perfect picture of calm, but Muzan could see minute twitch of his face muscles. Like he doesn't know how to react exactly. Understandable, because if Muzan have a twin who turned people to demons while he somehow become demon slayer, he'd be confused too. Maybe. Or he doesn't care much.

"He's you Slayers's problem." Muzan said, grouchy from his aching limbs.

"He's _your_ student."

"He's _your_ twin brother."

"You _created_ him."

Muzan didn't think this man could be pissed, but there it is, a frown. He raised an eyebrow, voice sounding bored. "And? I did what he asked of me." Without payment, no less. "Apparently he tried to kill me by sending you my way. Why don't _you_ kill me?"

"You're a decent human being." Yoriichi said, not missing a beat.

Muzan _snarled_. "I'm a _demon, you fool_."

Yoriichi shrugged, as if saying 'whatever you can do with it?' and say, "A decent demon being."

He was pretty sure there's something wrong with Yoriichi's head somewhere. Some screw loose maybe. No wonder Michikatsu naturally pissed at him every day, every time, every little mention of him. They don't made for each other.

* * *

Yoriichi followed him. He wasn't obnoxious enough to follow him when he have night classes and researching with Tamayo, but Yoriichi still followed him. Muzan was determined to ignore him, though. He will probably be gone taking care of other demons right?

But after two weeks, the man _still_ following him like a puppy, Muzan _snapped_. He dragged the man with a force he was sure breaking his wrist, and drag him down to nearby tea house. Muzan needed tea to be civil, even though he wondered why he even _need_ to be civil, King of Demons and all those fancy titles the Corps gave him.

_Don't you want to go out, Muzan-sama_, Nakime had asked him one day, apparently boredom rotting her mind just as his, _don't you want to go crazy apeshit sometimes_?

_I do now, Nakime_, he thinks, sipping his tea, _particularly including snapping this sun idiot's neck in half_.

"Do you have no other demons to hunt? Other things to do than stalking me?"

A pause. "No."

Muzan squinted at him, a glare which would render his demons to submission. "What kind of Demon Slayer are you, taking vacation from hunting demons?"

"I was kicked out of Demon Slayer Corps."

Muzan snorted. The guy must be joking. The silence stretched—Muzan looked at his black eyes, and realized with dawning confusion that Yoriichi was serious. The Corps was ready to kick someone as strong as this guy because his brother has become a demon? A guy who made the sun itself his blade?

Humans. Ridiculous, greedy, scared things.

"It's fine."

What?

"It's fine." He repeated, tone still monotone.

Apparently he had said that out loud. "I heard you the first time."

Yoriichi was looking at him strangely then, and Muzan is ignoring it by sipping his tea again. "You're a kind one." The slayer said, soft enough to be carried out by the wind, but it was loud and clear for Muzan's sensitive ears.

He almost choked. Almost.

Choking was beneath Muzan though, and he set his cup of tea down, delicately. His red slitted eyes appeared, face contorting to another snarl with elongated fangs as he glared at Yoriichi.

"Do not test my patience, Slayer. What is it do you want?"

Not bothered or flinch, Yoriichi replied, "You know where my brother is."

"Indeed." They still have a telepathic connection, though it was weak as Michikatsu actively blocked him out. Blood still sings to blood, though. _His_.

"Tell me where he is."

Of course. Stupid twin brothers.

Muzan closed his eyes, concentrated on his bonds to his demons, to Michikatsu in particular. It was not surprising, but still upsetting, when his bond with him was hazy. Like there's a fog surrounding him. He can't detect or see anything. This usually means he's away from Muzan, too far away, but it could also mean the other side is trying to cut him off.

Now he could only give a vague direction on where to go.

"South." He said, once opening his eyes again.

Yoriichi looks on blankly.

"That's the only thing i can give you. Your beloved brother blocked me out." Scoffed, as if Michikatsu could do that for long, "Now scram, slayer. And never return. Consider this payment of your idiocy to spare my life."

The Slayer looks amused, folding his hands under his red haori, definitely not going to go away soon, to Muzan's exasperation. "You want to die, though. You gave up on our battle. Why?"

Deep breaths, Muzan, deep breaths. One, two, three, four, five...

"If you really want to die, why don't you just stand under sunlight?"

_Fuck this guy_, he decided.

Muzan shot forward, not enough time for Yoriichi to duck, and he easily feed his blood on the Slayer's bloodstream. Yoriichi fell to the tatami, choking and convulsing, his hanafuda earrings clinking as he struggled. Muzan watched with bemusement and satisfaction rolling him off in equal measure. To the user of Breath of The Sun, how will his blood, the very antithesis of his Breath, react? Will Yoriichi just fell dead? In coma due to contradiction?

He watched, sitting back down and sipping his tea serenely, a total contrast with the sound of thrashing and choking in their little, private tea room.

* * *

Yoriichi Tsugikuni did turn to a demon.

Unlike his brother however, he did not undergone any transformation except his elongated fangs and nails. Muzan was sure he feeds enough blood in that short time, but as if his blood was burned by the sun, it held no effect whatsover to Yoriichi. No bloodlust, no crazed looks or losing memories. He is still the same, expresionless Slayer of The Sun.

_What the fuck?_

Muzan thinks, watching the Demon Slayer turned Demon actually sunbathing on his porch. _Sunbathing_.

It seems like the universe is determined to not let Muzan pass his What The Fuck stage of his life.

* * *

And Yoriichi Tsugikuni did not leave.

Muzan was fed up enough that he battled Yoriichi to shoo him off, like shooing a very violent chicken out. Yoriichi was defeated repeatedly only because he isn't used to his newfound strength and speed, seeing him fumble was fun, slamming him to nearby and through walls was enough to make him grin in glee. After first several battles though, Yoriichi learned; and he learned _fast_. He returned to his feet and proceeded to give Muzan another beating of his life.

Anonymously they agreed it's kind of a spar; a very deadly spar, but a spar nonetheless.

Eventually, Muzan decided, Yoriichi is like a mold. No matter how he scrubbed it off he would always come back. Or a weed. Or cockroach. The point is, he would let the man around. Besides, its not like he ever did shoo his demons away when they visited.

Besides, Muzan wouldn't say it out loud; but Yoriichi is a lost man.

_(Guess you picked up another stray, Muzan-sama,_ Nakime says, in a strange tone of hers when he turned another dying orphan on the street to demon on a whim.)

Muzan didn't realize it at the start, but the man was downright suicidal. When they sparred, considering Yoriichi is a demon now, Muzan was dead serious, and far, far more ruthless. And even then Yoriichi did not afraid to sacrifice his limbs for a win. As if he had nothing more to live, except a spark of determination and purpose; to kill his older brother.

But right now, right now Yoriichi would win for sure. Michikatsu did not win against Muzan, but Yoriichi did, and thus Michikatsu would be ultimately defeated. And Yoriichi doesn't want that, Muzan realized. That's why he doesn't seek Michikatsu. He wanted to kill him but also, he wanted to die in the process. A stupid honorable man.

Between him and his brother, who was hellbent on defeating him, it seems like Muzan has a penchant for picking up idiots.

* * *

Author's Note:

I have posted this in AO3 before, but maybe it's a good idea to also post this here?

This fic is a massive canon divergence, would be focusing on crack; especially how the demons and the world reacts to this Muzan who is still a cruel demon but ultimately is just some immortal guy who is bored out of his mind, featuring the legend OP good guy who also become immortal and is now Muzan's only moral compass. I am excited of this fic, so i'm hoping you guys are too!


	2. Chapter 2

Muzan was sure Yoriichi was not going to leave.

He had made himself a permanent resident of his current house, even Muzan considered rolling him in education just for the hell of it. They don't talk much, mostly bickering before one of them snaps (usually Muzan) and break something (usually Yoriichi's fingers). But Muzan understands Yoriichi and Yoriichi understands Muzan, much he loathed to admit. For Muzan, life is going too boring and he is desperately escaping it, often times with bloodbath which made him loathe life more at the end of it; and for Yoriichi, life has lost its meaning but one in the form of his rogue brother and he is willing to wait for as long as it needed to end life together with him.

(A couple of sad men they are, he thinks wryly.)

But one day, Yoriichi disappeared.

Again, Muzan doesn't keep track of his demons too much, they are adults on their own. So he didn't even bat an eye, and continue on his life. Because for once, something has happened in his life.

Tamayo has gotten sick.

And she has not getting better. Bedridden, her fever ups and downs for weeks, she hardly able to eat anything, and her skin pales to paper and body thinning to skeleton. It was as if he was looking at himself, decades (or hundreds?) years ago. Muzan also discovered that by far, he is the only one who visited her. They both never talked about family, out of respect of each other's privacy, but it's clear that Tamayo is also alone. In her quiet house, he did not see any indication of other human beings living with her, and traces of what he did in her house (like leaving dirty plates after he helps her eat) was there for days. So, not even a servant.

He's getting sentimental himself, Muzan thinks. Normally he wouldn't bat an eye to any sick humans he knew; all his demons was turned simply by his bored whims. If he can turn people to mindless savage murderers, he had decided long ago, at least he can be somewhat fair about it, not only picking the sickly ones or the rich ones. _Somewhat_.

But Tamayo is a really kind woman. This might be his sentimental emotions making appearance unexpectedly, but Tamayo is by far the only one who managed to keep up with his wit, his curiosity, even humoring his morbid and less than morally acceptable ideas. Tamayo is—and Muzan won't ever admit it out loud—fun to be with.

In no way he would ever let Tamayo die if he can help it.

And so, turn Tamayo to demon he did.

Apparently Tamayo had taken a liking in calling him 'Muzan-sama.' In fact it was the first thing she said after she woke up, all healthy and every inch a demon.

Tamayo knew it did nothing but piss him off, coming from her, _his mentor_. She took great joy in calling him like that every time, and since he likes Tamayo, he lets her be. Muzan thinks it's a way of her revenge that he made her unable to taste sunlight and become an abomination who needed human meat to survive, no matter how grateful she is.

Despite his annoyance, Muzan privately thinks, _g__ood then_. They can be salty about never able to enjoy _hanabi_ together.

* * *

Nothing happened after that.

As usual he didn't count how many years have passed in his life. They moved together, traveling around Japan (again) and studying a lot of things (again). Sure, it was mostly things he already knew, but having a constant companion like Tamayo make all the differences. Her mind provides new point of views and other informations he had missed before. During this less than boring time, Yoriichi has returned. This time, without his hanafuda earrings.

Perhaps he made a family. Or found a successor. Muzan didn't ask, Yoriichi didn't explain. Yoriichi simply fits as a third person in their little traveling group without explanation.

To Muzan's irritation, Yoriichi warmed up almost instantly with Tamayo. They are both partners in looking at Muzan with this '_Is This What You Call Morals?_' stare. Or in Tamayo's case, it's more like '_I did Not Accept You Being Messy In Muders_' look.

Since Yoriichi only needs a month or so of hibernation and doesn't need human flesh or blood to survive, he is the only one who remains Straight with his morals. Tamayo would be swayed with research and knowledge at the end of blood rainbow, sometimes. And Muzan decided he would conveniently forgot about morals once he is too bored.

(_Yoriichi stepped to the clearing then, wind swaying his long hair gently and the moon shines on his face, paling them. He is using that Look on him, Muzan thinks, and he threw a femur boredly from his bloody stone altar, done chewing the flesh._

"_It wasn't me."_

"_Really now?"_

_Muzan pointed a manicured index finger to the woods, to the sound of faint screams. Blinking slowly and innocently at Yoriichi who is coming closer, he nodded._

"_This is their doings, i'm just taking some meat, really."_

_Yoriichi, never deterred by his acting, slapped the back of his head. Muzan hissed and crushed Yoriichi's fingers to mush in retaliation. Yoriichi, still undeterred by pain and still on his Disappointed Look, proceeds to __drag__ Muzan away from the bloody clearing. By __Muzan's__ collar. The nerve of someone who can beat __him, the Demon King,__ to the ground, people. It was __only __the fact that Muzan was happy enough from chewing some eyeballs earlier that he let Yoriichi drags him._

"_Tamayo-san would _love_ to comment on how messy you are." Yoriichi dryly said._

_Muzan glanced to his clothes, soaked to the __skin__ with blood; even his__ normally smooth__ hair are caked with blood. Hm. Tamayo would go _batshit_ at this. In her own creepy-ish way._

"_Spoilsport." He said in the end, deadpan and resigned to his scolding_.)

And Yoriichi would not hesitate to beat him down if he ever dared to follow his whims and slaughter a village for his amusement. He doesn't care if that village constantly produced best pickpockets and underground criminals, no, Yoriichi only cared when Muzan decided to slaughter them. They would dance in a deadly spar through the night, and by the time the sun has risen Muzan has forgotten all his bloodlust born of boredom and only want to sleep for the entire week—which, he does. They don't do this often, because aiding Tamayo in her ever growing research about poison and genetics managed to distract him from boredom. It helps that once in a blue moon he can sneak away from Yoriichi, too. But when they do fight, their battles are beautifully devastating. It was the norm that they quickly move away to another city after their fight, because Demon Slayers would come sniffing trails of their battle.

Muzan thinks this might be Yoriichi's way of brooding revenge; he did curse the slayer to eternity and turn him to become something he had sworn to destroy, after all. By chasing him around and being his moral compass somewhat, Yoriichi have his revenge. For eternity.

Joy. At least he's a decently deadly distraction.

* * *

Muzan found Akaza as a half-mad human, attracted by the smell of blood from his slaughter in what Muzan assumed his _dojo_. Even as a human, he had this crazy look on his face that told Muzan of 'psychotic murders.' After all, the man did slaughter everyone with his bare hands; punching holes through people's chest by his fist, humans dropping like broken red-splattered dolls around Akaza. And so Muzan thinks, what better way to appreciate his martial prowess than to enable the man for more murders? With more firepower for his martial arts, too. Win win.

(Yoriichi's Look of Disappointment pops up in his mind and Muzan shoo the image away.)

He expected the man to be completely amnesiac after his transformation, but not to the point that he forget his name completely. Most of his demons still retained fragments of their memories after their transformations, including their names; not a blank slate like Akaza was. Puzzled, but still thinking up for a name, Muzan had said, 'Akaza.'

The newly-made Akaza had _beamed_.

... It was one of Tamayo's cats's name, that orange pudgy cat.

Not knowing his true namesake, Akaza is instead a true puppy. Akaza barked—talked—a lot. He asked things about Muzan and demons and sometimes himself, and he took his words to the deepest of his hearts, hanging by them like a life line.

("So you're my savior." Akaza said, flitting his eyes from the littered corpses and him. He seems to be thinking, after Akaza's barrage of questions stops and Muzan was done explaining and answering. Muzan's answers consists of a lot of 'I don't know's because he really doesn't know shit about this man. He was just attracted to smell of blood like children was attracted to candies. Akaza asking Muzan about his own background? He really doesn't know anything.

Muzan hummed. "Perhaps."

Akaza flexed his fingers, staring at them. "And you are—i became strong because of you."

Not exactly. But would he tell that?

"Then i'm indebted to you for eternity. I shall do my best to serve you. I shall strive to be stronger and stronger, Muzan-sama!"

Muzan blinked. _Too bright_, he quietly complained in his mind. Is that—_are those sparkles_?)

After Akaza was cleaned from blood and properly dressed by a fussing Tamayo, Yoriichi also treated him exactly like a puppy. Akaza was shy at first of head pats from Muzan-sama's friends, but he quickly warmed up to Yoriichi after their first spar. It looks like Akaza became Yoriichi's fanboy or something; the faster Yoriichi knocked Akaza out, the more spirited Akaza become. And to spite the swordsman, Muzan gave Akaza more and more blood until he wasn't defeated in the first thirty seconds by Yoriichi.

Muzan had looked smug when Akaza was finally able to _judo_ flip Yoriichi several hundred of meters away, to Yoriichi's amusement.

Akaza had then appointed himself as Muzan's _Number 1 Servant_ after that, in which Tamayo giggled and Muzan had given the man an appreciation head pat. Muzan could still imagine the ensuing sparkles and grin Akaza gave to him that day, when he closed his eyes. It was _that_ bright and _that_ traumatic.

(_"And you said he's _my_ fanboy." Yoriichi dryly commented._

"_Ever consider shutting up, you shitty one man peanut gallery?")_

And so their travel around Japan continued, this time with one more member in their ragtag group.

* * *

Not too long after that, Muzan found a Cult.

And as per Muzan's Standard Protocol, he hunt them down and proceeds to pick few for dinner and then a few more to be demons. He would then sat down calmly as he watched the carnage unfolds then mutilated some body parts for him to bring back. Nice to know he doesn't have to eat one week old corpses which Tamayo insisted are 'food.' Old-age eyeballs didn't pop the right way in his mouth, and if they are preserved they have the weird taste of chemicals. These ones, however, are _food_. They are succulent, sweet, and fresh. Sometimes they taste of something the human had eaten before, like this one, tasted like alcohol and fish. Sushi?

... It sounds like he's talking about fruits, so moving on.

As he was sitting down on the altar like a newly summoned demon, chewing on human thigh, he locked eyes with a blonde man.

That weird blonde man with rainbow eyes, who smiled and stood still like some sort of creepy doll the entire time he watched his Cult friends was slaughtered; is Douma. Douma ignored his cult friends even when they beg for help in front of his face, resolutely staring and smiling at Muzan. If Douma hadn't blinked, Muzan would've thought he's a statue.

Douma is a very creepy human, he did not react at all when Muzan stabbed his thumb to his wrist; mind, at this point they still are staring at each other. Douma simply transformed, not breaking eye contact, with no convulsing or choking scene. Realization of being a Demon had come to him like an information of the changing weather and Douma had happily followed Muzan in silence. He smiled the entire time.

For Muzan, Douma is a creepyly handsome Doll.

He just _exist_, _there_, quiet, and when he talks he usually says something friendly, a very creepy or downright shitty joke, or say something polite, but his expressions are very fake. It's like he's a life-sized doll equipped with friendly dialouges and crack psychopathic puns. Even Yoriichi is unnerved by Douma. For Muzan, Douma is _fine_ because Muzan lives and thrives with weirdos his entire life. His demons are all weirdos, in one way or another. There's this guy who ate origamis in blood for fun, another one who _loved_ to make lanterns of eyes (said it's aesthetic or something like that), Akaza loved cleanliness and cleaning in general Muzan doesn't know _why_; even less on why Akaza would specifically hum _kabuki_ songs while he pulls out weeds and the Shogun's anthem when he sweeps the floor, Nakime may look normal but she loved to paint using blood—insisted to make and discover wonders of red (whatever that means), but all her paintings are _Red_, Just Red, no matter how she insisted how many different shades of reds on her painting. Tamayo is Tamayo and Yoriichi is Yoriichi; enough said.

And Douma is in his own League of Weird, sure, but Muzan is totally fine with that.

(_"As my thanks, i will give my heart to you, Muzan-sama!" In which Douma promptly dig a hole in his own chest with his bare hands, pull his heart out in a spray of blood, and knelt in front of Muzan. He is grinnin__g and he tilted his head to let his eyes sparkles rainbow__, which means this is his idea of a joke._

_Akaza twitched violently due to the mess. Tamayo and Yoriichi looked at Muzan in Accusation, of _'What The Hell Did You Teach Your Children_?' look. It's not Muzan who taught Douma his sense of humor, though, he developed it himself._

_Muzan, ignoring the three, had simply said, "I already have five of those, Douma."_

"_Ah I see. Then I shall give you ten!"_

"_Please don't, Douma-kun." Yoriichi had said, and fortunately Douma had listened_.)

For Akaza and Tamayo however, Douma is Trashcan.

Akaza because he downright Loathed (yes, the capital is important) Douma's existence in general, and Tamayo because she could infuse whatever leftover of her toxin experiment (which she couldn't throw away due to environment hazard) in human carcass or corpse and Douma _will_ eat that. His inability to feel pain is very useful as it put Tamayo's mind at ease. It's not even his Blood Demon Art, he isn't even a gourmet, but Douma has a believe that whoever humans and remnant of humans get eaten by him and Muzan are thus saved from this shitty world. Muzan draw the lines on bones, because Muzan is a lazyass who refused to do more than bare minimum in chewing and refused to choke while savoring his food, but Douma will make bones smoothies and drink that if he can. As it is now he just chew them like popsicles. Muzan wondered if Douma intentionally strengthen his teeth for that, then one of his brains would provide a memory of Douma literally chewing glass and steel container to get the preserved human fingers inside and… yes, he probably strengthen them.

Tamayo took great joy of Douma the Trashcan, of course. She has been curious on what poisons and combination of poisons she could make, but she has been hindered by environment hazard. Douma is happy (actually hard to tell with the guy, he's a standard smiling doll) to help expand Tamayo's curiosity, not caring about said hazards anymore. Akaza reigned down his violent outburst when Douma is on experiment with Tamayo, but he Will pulverize Douma's head to blood in their garden. When Muzan asked, Akaza replied,

"He's—he just—pissed me off, Muzan-sama! He doesn't—the bastard has no value whatsoever. He's _empty_. And he pretended like he isn't! When i see him i just _had to_ punch him."

Douma, with reformed head, merely widens his smile, "You're such a _good dog_, Akaza-kun. If you're a woman i'd even say you're cute!"

Douma lost his head again in a second after that comment, to Yoriichi's disapproval. They had continued trying to kill each other until Muzan had to physically separate them with his tentacles and assign them on different tasks. Over time, Yoriichi also took charge of separating them. Muzan privately thinks it's like owning a dog and a cat who fights each other a lot. They do learn to be peaceful in Muzan's presence though, so that's an improvement.

And thus, the group continued their jouney, with one more weirdo in tow.

* * *

Naturally, Muzan met Michikatsu again.

You see, when you live as long as him and has a shitty sense of time as him _("How's the Ubuyashiki, my cousins? Didn't their eldest die of heart failure months ago?" A pregnant pause, before Nakime replied, "No one of the Ubuyashiki died of _heart failure_ since fifteen years ago, Muzan-sama."_ ) you will eventually accept that you will meet the same people or descendants of same people you have met years ago, one way or another. This world is small, no one dared venture outside of ocean, tragically, the emperor is a coward and fool to not ever try, _this_ _world is small_, so of course Muzan and Michikatsu met again.

What Muzan didn't expect however, how he was ambushed by ten or so demons, plus Michikatsu himself.

Now Muzan is no slouch, he is a nerd, maybe, but he can lift his own weight in a fight. It's just he doesn't have a _nichirin_ blade at his side, and these ten demons are far more skilled than usual hungry demons. They _reek_ of human blood, each one of them. Reek of slaughter. Powered up, if you will.

The battle was amusing, at the start. They are still such easy targets for Muzan who is used to Yoriichi, the embodiment of everything a deadly fight can offer. His hardened hair would struck them and line them up like meat and Muzan is happy to gauge their eyes out and use his bones as projectiles to pin them to trees. But they come back again and again, and mind, there are _ten_ of them. With Michikatsu, the fucking asshole coward, who will use any distractions provided by these demons to cut Muzan down.

In the end, pulling a spine off of a demon after decapitating it, Muzan was faced with Michikatsu and one stray demon. Bloodied, definitely pissed, and full of wounds which stings his blood and nose (interesting, his blades must be imbued with _wisterias_, damn him), Muzan stalked to his first disciple.

"Fancy to meet you too, Michikatsu," Muzan began, because his mother never taught him to be rude asses like these Tsugikunis, "I see you still can't kill me." He grinned, bloody teeth and red eyes shining under the moonlight.

Michikatsu flicked his blade, the only indication that Muzan did annoy him with his remarks.

"We shall see." He said, walking slowly, confidently, to where Muzan stood.

Much as he loathed to admit it, Michikatsu _would_ win this one. These cuts aren't necessarily painful, but they are restricting as they are laced with poison. Muzan's body is stiff and his eyesight is starting to blur. And Michikatsu had, somehow, become faster than before. In any other situation Muzan would be proud, he would praise Michikatsu of his progress, but this is life or death situation and—

_And… what_?

Since when did Muzan does _not_ want to die? Since when did living become a bit bearable, even with full realization of his sins and conscious murders? Since when did his ignorance of his demons's manslaughter has become easier to the point that he had accepted it and even content with it? With what he have right now? Since when did his consciousness feel this… _light_, of the world? Who took the burden from him? Didn't Michikatsu just fulfill his end of bargain now, even with dirty means as it is?

Pain blossomed in his chest then, he looked down to see Michikatsu's _nichirin_ cut to one of his hearts; _left atrium hole-right ventricle-heart valve tear-poison to vena-__unsalvageable_ and _left lung tear-intermediate lung failure, _Muzan is thankful he equipped his Doctor Brain in his head right now. It has automatic professional doctor response to kick him out of his crisis enough to hone his hand to Michikatsu's throat, forcing the man to jump away. Deflected his Breath of the Moon with whips from his back, Muzan struggled to stand up.

Wisteria poison, he could feel, creeping his bloodstream from his heart and he coordinated his second brain to independently replace his heart and took control of his bloodstream, half of his spine, to quickly flow them out of his wounds. Taking a page out of Warrior Tales, Muzan blabbed out mid-battle. From his blabs, he earned; 1) Michikatsu's aggression, 2) decapitated left hand and right foot, hard to regenerate with so many poisons in his bloodstream, 3) Michikatsu's monologue of saving the world by conquering it.

"Humans are weak. They are created to suffer with such weakness. I shall free them of their weakness and despair and I will rule atop all of them. Being demons, they will be controlled. Everyone will have their peace and power to prove and protect their own justice." Michikatsu said in the end, after he recalled his travels and see a lot of poverty, war, suffering demons, orphans, and what not.

And, honestly, _what_. Just _what_?

Muzan didn't teach him philosophy as his mentor, sure, but he didn't think the kid would be this _naïve_. But again Muzan surprised himself by holding his tongue and not voicing his thought.

Michikatsu finally knelt in front of him, a scowling bloody mess Demon King.

"As I expected, you did not agree." Said Michikatsu, flat, his six eyes looking at him with no emotion.

"I have been many things in my life," Muzan bared his teeth, smiling, blood dripping for his lips, "but a _fool_ is not one of them, boy. Even after all this time, you are still a _weeping_ _boy_ seeking for empty justice for your own; and when you did not find it, you blame it on the world and forced your way with childish _tantrums_."

Before a Pissed Off Michikatsu could kill him, Muzan's hovering tentacle strikes Michikatsu's neck first, feeding more blood to him in spite. And because it's the only thing Muzan can think that could cancel his Final Moon Breathing stance. What, he thinks Muzan didn't notice the inch shift of his blade, the minute change of pace of his breathing? Try again, Michikatsu.

Michikatsu drops his nichirin and writhes in pain. While he does that, Muzan quickened his foot regeneration and forced himself to stand up and Get Out of this place. The Sun will rise in one hour, Michikatsu will rise in even less time than that and Muzan have to move _fast_.

Muzan remembered running through pain of poison choking his lungs, remembered honing his nose through the poison to find his current hide, and the last thing he remembered is Akaza's startled look morphed to a fierce snarl, and then he collapsed.

* * *

The sky was dark and he could see the moon when he woke up, staring at the ceiling of his own room. Muzan could feel his own futon behind him, and slowly he sat up.

He already registered Tamayo's presence beside him, apparently she's putting down herbs and old bandages soundlessly. She didn't ask what happened, and he's grateful for that. Muzan is angry—no, he's downright _pissed_, as his brain recalled his fight with Michikatsu and what he implied. He's also berating himself for being an enabler to Michikatsu and his newly megalomaniac ambition.

Why couldn't he just think of better things tan feeding more blood?  
Why couldn't he just let himself died then? Is he that pathetic to be afraid of death now?

Muzan doesn't know if he could speak clearly and not lash out right now. Tamayo really knows him well.

Coming to a conclusion and a plan, Muzan closed his eyes. Through his telepathic bond to his demons, he reached Hitomi, one of his demons with a particular Demon Blood Art of mind communication and mind-control unlike of his own. He told the spooked demon to contact every demons in several locations too far from his reach to go to Natagumo on full moon, trying very hard to keep his mind voice level, but it seems like he failed by how Hitomi screeched a bit. Next he contacted Nakime, to meet him in his current hide.

Then, he concentrated further.

He reached every demons he can reach—those far away or not—and Muzan registered how Tamayo stilled as he opened his connection to her. Dimly he also recognized how Douma's and Akaza's quiet bicker in the garden recedes, and Yoriichi's footsteps in the hall stops.

"_Mount Natagumo. Full Moon. You will come or you will be hunted and face an agonizing death."_

* * *

Surprisingly, even Yoriichi understand when he wants to be left alone. The man simply take Muzan's silent request for peace as a time for him to hibernate.

Three days of waiting for full moon spent by Muzan recovering; mostly sleeping, eating corpse-fused medicine, and then went back to sleep. Those wisteria poisons are a bitch to be flushed out, but he and Tamayo already worked for combination of herbs to thaw that a few months ago thankfully. His house is quiet and Muzan is silently grateful for Douma's and Akaza's understanding of his condition. Or maybe they're just plain scared, that's a possibility too.

Nakime arrived the night before meeting, and Muzan just feeds her a drip of her blood, to her quiet surprise.

The six of them moved to Mount Natagumo at night and settled deep within the forest, nearly at the top. He ordered Nakime to activate her Blood Art until it reached all of the mountain's region and outskirts, and ordered her to take any demons who stepped to the mountain in her Interdimensional fortress.

It wasn't until fifteen minutes of waiting that he had all of his demons—seventy five them and then _some_ additions he expected—kneeling in rows and rows in front of him, inside Nakime's fortress. Even Yoriichi and Tamayo knelt too, even if they both do it more for amusement and curiosity. Muzan honestly didn't mind if they chose to sit beside him on the platform, but this is alright.

"Some of you have _dared_ to betray me," he said, quietly gleeful in his demons's frightened surprise to realize that a petite girl in flower kimono is actually their _creator_, "insufferable, ungrateful _ingrates_," he spat, "and I would like to show all of you how merciful I am to them."

Muzan caught one who trembled; one he doesn't remember turning himself, and his tentacles caught her, hauling her up in her neck as she thrashed and cried.

"Quiet, girl." And she did quiet, significantly, to whimpers. "Now tell me why would you follow _that man_ and betray me."

Between hiccups, she apologized. Between sobs, she begs that she doesn't mean to betray him, and Muzan put a show of listening to her in pity and started to lower her down to the ground. He lowered his grip on her neck and she _growled_, breaking free and grinning in triumph. As expected of bad actors.

"You have no ambition!" She sneered, "Kokushibou-sama was right! Your power is wasted on a weakling like you! Kokushibou-sama will rule this world to bring salvation to all of us! And you will be slain by him you weakling!"

Then the fool actually dared to jump and stretch out her Blood Demon Art by the wild strings of her kimono, homing to Muzan. He didn't even blink when Douma cut them down; her strings, her head and her torso, and Muzan let the doll gnaw at her remains as he returned to kneel. The bloody mess made Akaza beside Douma twitch, but otherwise he was quiet and bowed his head down.

Muzan let Douma ate her bones in peace, letting the crunches of bones grinding to pieces in his mouth echoes in the quiet, horrified atmosphere. At the same time, he mulled over her words. It's true he didn't really try to be cruel lately, he's bored of it. His demons hadn't increase in number, cumulatively they're decreased even, what with Yoriichi hunting him down. And maybe Yoriichi finally affect his morals too much if his demons managed to think of him as _weak_. Muzan had no doubt there are a few other of _his own_ demons who also think the same.

"Do you think of me as a fool?" Muzan eventually asked. "Do you really believe on her prattle?" A pause, before he channeled his chilling rage to his voice, "Or do you think by staying quiet you would get out of this alive?"

His tentacles reached two of Michikatsu's—now Kokushibou's—demons, and few of them jumped away to the depth Nakime's labyrinth. Those, Nakime redirected them straight to Douma's jaw and Akaza's fist, a bloody mess for the front row demons who trembled in fear.

The ones who Muzan personally made demon kept their head bowed deeper, while those of Michikatsu's gave up struggling or begging, began honing for his head. Surprisingly, some of his own demons also attacked him, probably in the same belief of the demon girl earlier. Between Nakime, Akaza, Douma, and himself, they managed to make an impressive rain of red for the whole wooden floor. Muzan almost regretted it when Tamayo looks stone-cold pissed because splatters of blood on her hair and kimono. Seeing Yoriichi deadpans and staring ahead (probably contemplates his life) was worth it though.

"Now," Muzan said, extending one fifty tendrils of tentacles to stab each one of his demons excluding Tamayo and Yoriichi, "if you dare to speak of me or Kokushibou you shall die." He added new drip of blood to them to strengthen their connection and their thoughts to Muzan, plus a curse that if they dare to even speak his name or Kokushibou, they will explode instantly. A memory of Kokushibou's appearance and skills is also given, to let them know what to watch for. A tattoo mark of tiny red crescent moon appeared on where he had stabbed them; a claiming mark.

Muzan waited until they stopped choking and back to their kneeling position, "If you see any demons who does not bear the same mark on you fighting a Demon Slayer, you should fight that demon off the Slayer. Bring that demon away from the Slayer, and kill them swiftly. Do _not_ harm the Slayer along the fight." Startled, Yoriichi looked at Muzan, but Muzan ignored him. "In doing so, I would grant you with even more of my blood. I will behead you myself if you dare lie to me about this."

Because Muzan could see some contempt and confusion on his demons (even beginning of a sneer), he continued in a chilling voice, "I have spared your life. I have gifted you more of my blood. Do you mean to tell me you _cannot_ fight a demon while fending off a mere _human_ at the same time? Do you mean to tell me you can't even _outrun_ a human?"

It's unfair, he knows. Some of the Slayers are tough, especially with their _nichirin_ and their Breathing Technique. But Muzan liked his demons with high quality than quantity. If they can't do this then they can die.

And if Muzan ordered this because Michikatsu chose to be a bitch by completely blocking their telepathy connection (how did he manage that, Muzan is still curious) and declaring war on him, nobody needs to know if Muzan is replying it in kind.

"Perhaps I should have killed all of you, then."

By his musing, he saw all protests died down in his demons's expressions, only complete obedience and a bit resignation. Good, good.

"I expect good news to come."

Nakime recognized parting words when she heard one and she strums her biwa. At once, his demons are out of the Interdimensional Fortress. Yoriichi, Muzan, Douma, Akaza and Tamayo are the only one who remains.

"Akaza, Douma." Muzan said, mildly pleased to see the both of them snapped to attention instantly. "Find me Blue Spider Lily. Find information about it. I suspect it's a herb, possibly a flower, but it could be gems, animal, or something else entirely. Do not return until you find information on it. Douma, do not get distracted. I _will_ know."

While Douma was slightly miffed (a microscopic twitch on his widening smile) on being called out of his plans to laze around and developing his cult for his personal food and entertainment, Akaza frowned and looked ready to protest because he doesn't want to leave Muzan. He knows Akaza can work it out alone, though, so he left him be. As a parting gift, he feed both of them with more of his blood, adding kanji 'Moon Two' and 'Moon Three' respectively on Douma's and Akaza's left eye.

"I will be in contact."

Again, Nakime strums her biwa and the both of them disappeared.

"Tamayo," Muzan said, stepping down the stair and ignored her slightly pissed off expression when she raised her eyebrow at him, "ever wonder how did humans turn to demons? Think it's reversible?"

Tamayo's violet eyes lit up with a small curve of smile on her face. Definitely already ahead of Muzan in researching those. Muzan knew he will be run through the ground for research by her like his university days, _again_, but well… with Tamayo, he knew this will be nothing but fruitful.

* * *

A/N

Next chapter, I swear we are entering canon. Tanjirou will meet Muzan and Confusion among Demon Slayer Corps will be shown. I'll also add interludes/prologues; stories on other characters's perspective on Muzan or on what happened generally. Also... this is a Fix-It, i'm trying to keep everyone alive by this.

Thank you for all your kind reviews! I hope you guys enjoy this update!


	3. Chapter 3

Michikatsu can do nearly everything when he puts his mind into it.

… That was an understatement. Scratch that, Michikatsu is an amazing, _terrifying_ person.

In twenty years after their battle, Tsugikuni Clan has gained fame as one the most powerful clan in Japan. Among with their fame is the circulating rumor that the Clan has used black magic or black priests to eliminate their rivals to reach the top. They aren't wrong per se, just nobody knows that a literal demon is behind the Clan's back, cherry-picking important figures of rivaling clans to kill.

It took, to Muzan's observation, a lot of information to decide who to kill in the hot mess people referred as Government Clan Politics Behind The Shogun's Back.

As a stranger peeking in, Muzan would have clapped if he isn't wary of the implication.

Michikatsu is eliminating every clans who didn't bow to the Tsugikuni and they are doing it beautifully. A kidnapping here, a stolen treasure there, a bit blood here, and a small civil war—and suddenly, Tsugikuni Clan has the Shogun's favor now, even the current Clan Head becoming a member of Shogun's advisors. Sure, the other Clans would probably investigate the suspicious deaths, but if they can't find the body then what can they do? If they only managed to find the remains, isn't it safe to assume a wild animal is the one responsible? Hunting trip gone wrong is common, after all. What happens in the forest stay in the forest, who knows what actually happened?

It's not like Demons are real, _right_?

On that note, with Tsugukuni's Clan position, Michikatsu even managed to cut out Demon Slayer Corps's funds.

Muzan heard this from one of his best spies, Gyokko. Since he actually managed to turn himself to a fish and then getting sold as an exotic magical art fish, moving from one rich pond to another rich pond, hearing things is his forte. How he did it without getting burned by sunlight, only God knows. Maybe he is truly magical.

Gyokko reported that Demon Slayer Corps are initially funded, following an extreme spike in Demon activities, murders, and overall bloodbath (Muzan faintly recalls it as his Dark Age, or maybe the Beginner Phase, since he was so frustrated with his immortality coupled with scholarly stress he became trigger happy to turn everyone, it's an _embarrassment_) more than two or three hundred years ago. But since demon activities has lessened and technology moved forward, a lot of the upper echelons doesn't believe in demons anymore.

Coupled with Tsugikuni's Clan Head (read: Michikatsu's) insistent on abandoning the Corps altogether, the Demon Slayer Corps hardly get any funds.

Muzan promptly sent Gyokko to sniff on the Ubuyashiki's funds then. Confirming they still have support from Swordsmith village and more than a few small but locally influential Clans, Muzan sighed a bit in relief. At least they will survive for another one hundred or so years.

While listening to his demons's reports about Michikatsu spiked his anxiety and made his fingers itchy to punch things, Muzan hadn't do anything to stop him.

Mostly because it's troublesome, true. The work it takes to derail Michikatsu's machinations and covers his tracks so the humans and Michikatsu's demons won't notice him is outright ridiculous. It doesn't help that Muzan doesn't know the bigger picture, he doesn't have enough information for that. Sure, maybe Michikatsu wants to become the Shogun. And then what? Which village does he want to obliterate first? Which clans would agree, which would oppose? What are Michikatsu's micro-plans? How many demons are actually involved within the Clans? Do each one of Allied Clans has a Guardian Demon or something?

Its too much scheming, too much work, too much concern.

And so Muzan focused himself on research of his own blood. With his own blood, he could at leat try to find out how it could turn organic things to demons. With Yoriichi's blood, he could try to see the differences between his and Yoriichi's so they could isolate what is it in the Sun Slayer's blood that could burn his demon blood. While Muzan worked with his own blood, Tamayo worked with Yoriichi's.

They tried herbs, combination of herbs, and different methods of extraction from herbs and their blood to see their reaction. This research would take more than fifty years, maybe hundreds of years, and no normal human would try this. It's a good thing both him and Tamayo are immortals, their data are consistent and the research is continuous.

_Muzan-sama,_ the letter read, when Muzan picked the wrong paper to write his findings on wisteria with a small titer of his blood, _I have found a useful pet. I sincerely wish you could name this pet. It's Slayer's Crow, it followed me here after I failed saving its previous owner_. Ah, Muzan notes, red eyes flicking to the previously unnoticed crow perched on the lab's window.

"Hello!" The Crow croaked, and Muzan raised an eyebrow. Didn't know the Corps trained crows now.

"Hello." Muzan replied quietly, reading back Akaza's letter.

_Rest assured, I have punched the demon that killed the Slayer to pieces, it couldn't regenerate and I hide its remains out of sight, so that man wouldn't notice it gone for a time. I have unfortunately not met any progress in finding Blue Spider Lily. I apologize profusely for my failings._ _The crow is not named yet, I sincerely wish you would accept it as my penance of my failure_. _Eternally wishing you good health, your loyal Servant, Akaza_.

A name for a crow, huh?

"Neko." Muzan said, and the crow tilted his head. Parroting "Neko?" back.

"It is your name." Ignoring the crow's squawks of protest, Muzan grabbed a piece of paper to write instructions for more reports and maybe a bit espionage (Akaza can't keep quiet for long though) about Michikatsu to the demon. Shoving the letter to the indignant Cat the crow, he pushed the bird out of his window.

Now where was he? Right, boiled wisteria with his blood.

"You have a bad naming sense, Muzan-kun." Tamayo tutted from another side of the room. He didn't even notice her enter earlier.

A moment passed before he decided to reply, "It's funny."

"_Horrible_ naming sense. I shudder thinking of what would _you_ name our demon antidote."

"Thanks _shisou_, I _try_."

* * *

Every year, Douma would visit Tamayo and Muzan's house to eat leftover experiments per Muzan's order, like a convenient trash can he is. These visits are normally uneventful, with Douma chewing things and Tamayo or Muzan in the room, collecting and reviewing notes.

"Muzan-sama, what do you think of children?"

Douma usually come and go without a word, so when Douma spoke, it surprises Muzan enough that his pen slides and scratch the paper until it creates a hole.

Knowing Douma, Muzan chose to ignore him. He wasn't even looking at Douma as he picked another paper to write. And he waited.

"..Can I eat them?"

There it is. The real question he wants to ask.

Muzan thinks of the question for a bit. His demons are free to do whatever; collect eyeballs and intestines, become a fish, become a venus flytrap, makes a castle of femur—see, the limit is their imagination. So Muzan doesn't think he has any say in deciding what they want to eat or not to eat, tiny human beings or not. But personally….

"…I don't eat children." And he doesn't. He had killed children, overestimating his blood amount to their tiny body that they often explode, often times just smashing them too hard to things because they tried to attack him. But he doesn't eat them. He also doesn't care if his demons want to eat exclusively children, virgins, or virgin boys whose birthday is on October on full moon. We all have food preference here, no matter how weird it is.

Curious, Muzan peeks through his hair, noting Douma looking back with the same empty smile he always has. Douma nodded then, and said, "Of course."

Muzan isn't sure if he understands what Douma means by that _of course_, but he decided to let it go. Whatever it is weird thing Douma planned, future Muzan would deal with it.

* * *

"Who are you?" Yoriichi asked, after staring at his female, yukata-covered form for about five minutes since he entered and sat in front of Yoriichi.

Muzan forced himself not to growl, instead flicking a stray cut of ramen from the table to his forehead. As usual, Yoriichi didn't even blink.

The demon sighed, before changing his voice pitch to that of his usual self and said, "It's me, you idiot."

The man's mouth promptly made a genuinely expression with his mouth forming a perfect 'o' it made Muzan snort. Even after all this time, Yoriichi still didn't manage to figure him out if he's in disguise like this. Yoriichi truly walks the line between genius and an oblivious idiot.

A sigh. "Come on, we are going on an errand. Tamayo wants some wild berries around these forests area."

The errand itself is normal enough. Muzan directed Yoriichi on which plants have the berries that they want. It helps that they can ask the locals; nobody suspects a girl with a yukata with her onii-chan looking for wild berries to help their sickly auntie. Maybe a bit question because it's night, but the questions are tame enough with them convinced Yoriichi could protect them both. Besides, the night is still young. Sunset was literally an hour ago. Thankfully Yoriichi is quiet the entire time Muzan had to use his female pitch voice and he followed his cover story naturally (by being his usual stone self).

What isn't normal was a dozen of demons appearing out of nowhere from the foliage of the forest. They aren't Muzan's, as he activated his curse telepathically and none of them reacts. Damn. He had to find more ways to breach through Michikatsu's control of technically _Muzan's _demons.

They didn't even fight back to back, as Michikatsu himself appeared and separated Muzan and Yoriichi while cracking the ground and trees between them in several gashes.

Muzan vaguely noticed that Michikatsu and Yoriichi are in a duel, leaving Muzan with probably twenty demons attacking in unpredictable patterns. Dodging an exploding earlobe, Muzan parried several hair-limbs while his tentacles are busy on their own warding flamed nails, multiplying pens, and a lot more projectiles. He snarled when a rubbery foot curled around his ankle , cutting it to pieces but the time of stand still cost explosions and needles to his body.

Forcefully shifting his body mid-dodge, he unfurled a set of bat wings made from his own bones and skin from his back, and with a stifled groan of pain he flew up. Mid-air, he forced his bones to produce needles, and with a beat of his wings he rained them down on the demons. Bloodied, dead trees grew and twists like clay to reach him, twigs reaching out and throwing projectiles. Supported by sharp rock projectiles, needles, and poison fog, with gritted teeth he realized he has to come down. Muzan pulled a bone from his shoulder as a makeshift sword, and dive-bombed down to the one controlling the trees. Tentacles reaching out to impale everything in its path, the fight continues.

It was the most exhausting fight Muzan ever had the pleasure of participating.

Sure, in the end he barely end up with a scratch and other demons are in pieces. Sure, his pain is now gone and he returned to his usual condition, but it was tiring. What is Michikatsu's problem anyway? Muzan is kind enough not to do anything as of yet to their war status quo, and he replied with a direct attack?

Muzan limped to the clearing where the trees are slashed in at least twelve pieces and the ground burnt, twisting his ankle to drag his feet through the destruction Michikatsu and Yoriichi has wrought. The trees eventually stopped to find way to an open grass area, no less wrecked than the forest.

He was just in time to see Yoriichi stabbed in the chest by Michikatsu; his pale, usually expressionless face contorted in pain as Michikatsu pulled the blade up, through his lungs and out of Yoriichi's left shoulder. Dropping down like a doll, his black _nichirin_ fell from his remaining hand as Yoriichi coughed blood.

And now Muzan is exhausted and _pissed_.

* * *

It's funny, actually.

Muzan hadn't actually want to do anything about Michikatsu.

Sure, he wants to conquer the world and bring world piece. But there's one of his demons who wanted to make a brothel for demons, another who wants to be director of all swords in whole Japan, or marrying and eating all virgins in this word. So on so forth, he had heard a lot of other wishes and ambitions. What difference is Michikatsu from his other demons? Other than, you know, he's far more ambitious and idealist.

But this. _This_ is personal.

Yoriichi's second chance of killing his brother and died together with that shitty brother wouldn't end here. It couldn't. While Yoriichi hibernates (_for who knows how long, who knows if he will be awake ever again_) and recover his strength, Muzan would teach his first student a lesson.

_Fine_, Muzan thinks, looking at Yoriichi's pale face and Tamayo's exhausted one after the hellish operation to fix his lungs, ribs, and flushed the wisteria poison out with his critical condition, _I'll do this myself._

"Douma is close to Edo." Muzan offhandedly mentioned, fixing his sandal.

Tamayo stared at him for a moment too long, and Muzan realized she is worried. For this reckless plan of his, for this 'I'll travel around Japan again, alone, dig information about Michikatsu and makes his life harder whenever I can' hubris. Hey, at least he's determined to go through with this hubris.

Eventually though, Tamayo nodded. "Be careful." She said, her hands holding each other tightly and yet her smile remains serene. "I will take care of our resident Slayer of The Sun, don't worry. Edo is a nice place to begin contact with the Slayers."

Muzan raised an eyebrow at that. Yes, he does needs another person inside the slayer Corps for his Big Plan to be realized, but really? Tamayo is willing?

"I should hope so." He concedes. "I wish you luck, Tamayo."

"And I to you, Muzan-sama. I eternally wish for your success and eagerly awaits your return."

Hm that was very sincere of her, no trace of sarcasm or sassiness which usually is there. That's—hm. No. He's getting emotional. That's no good. After all, he has a lot of things to do.

"I'm going."

Muzan jumped to the trees and disappeared to the dark, not noticing Tamayo who bowed down deep to her waist.

* * *

_Muzan-sama, as you suspected, the is a demon under the Minamoto Clan's household. I have dispatched the demon and deliver the letter as you instructed. I will leave for Tsugikuni Clan come sunset._

* * *

_Muzan-sama, the girl wouldn't shut up, so I forcefully put her doll stuffing to her mouth. She seems to be fine, breathing and healthy, but I am not sure. I will arrive in the Tsugikuni this midnight._

* * *

_Muzan-sama, there is a complication with the doctor, he did not want to come with us. He seems to be scared of Douma. He fell sick seeing the amount of blood Douma has when his head explodes. I was forced to knock him out, but I did deliver him to the Midoriko Clan. My failure of disciplining Douma is unacceptable. I await your punishment for this failure._

* * *

_Muzan-sama, Douma have done killing the demon under the Ashiya Clan and I have dropped the letter. We are now on route to the Yoshida Clan._

* * *

_Muzan-sama, Douma have too much fun killing and eating people in this region. I sincerely requested he is put to a severe punishment for not doing his mission seriously. I made eye contact with the target as you instructed._

* * *

_Muzan-sama, it seems like the mission is success, the Tsugikuni no longer lives in the compound. Rumor has it they are exiled into another region._

* * *

_Muzan-sama, I have met with Gyokko as you instructed. The Demon Corps have regained their funds, spearheaded by Yoshida, Minamoto, Atsushi and Midoriko Clan._

* * *

_Muzan-sama, I have dispatched of the assassin residing in Nobunaga Clan as you instructed. Should I remain in the household?_

* * *

_No. Go to the Suzumi Clan. Kill the heir; male, first born, 20, go by Ryuuzaki and often boasts about boar-killing. He should be guarded by a demon. Kill it too. Nakime is in the region. 3 months. Don't leave any trails and don't be seen, or make it natural._

* * *

_Muzan-sama it's Douma. Make it natural means no trace and I can eat them all yes? Neko is such a bad crow he keeps biting me can I eat it and we get a new one?_

* * *

_Yes. And No. Play nice, Douma._

* * *

_Muzan-sama, I have captured and killed the traitor. There are several of that man's demons chasing me and I have dispatched them as well._

* * *

_Muzan-sama, we managed to track Ubuyashiki but were ambushed by Hashira slayers. We are injured but Nakime and Gyokko have accommodated our escape and we will recover fine. Unfortunately none of those ungrateful humans want to listen to us or accept your letter. I deeply apologize for my failure._

_They burned your letter and Akaza get angry he punched aaalll of them and they tumble down like treeeeesss, Muzan-sama. They aren't dead though, so they'll be fine. Probably._

Far in an inn, Kibutsuji Muzan sighed and pinched the bridge of his nose, exhausted. He let Neko in and ignored it as it drank water and eat some corns he prepared earlier. Well that's one failure, at least the other ones are successes.

Now… he has a heiress to frame.

* * *

"Muzan-sama, I have kids!"

"Put them on the table."

A set of thuds and a yelp—_wait what_?

Carefully, Muzan puts vials of blood down in the closet before he looked at what Douma had just put on the table of his lab. It is indeed, children on the table. Demon children, actually. Teenagers, maybe. 12? 13 years old?

Muzan twitched, resisting the urge to facepalm.

"Where did you find them?" He asked, flat.

"I was wandering around Edo looking for information as you instructed, and then I found them in the alleyway and they said they want to be demons. I asked and played nice." Douma said, sunshine and smile for whoever looked at him and not knowing what he is.

Muzan took the information for a couple of seconds before he looked at the children; male and female, both looking warily at him. But interestingly there's also contempt at the male's expression, contempt which he tried and failed to hide.

"Is that true?" He eventually asked.

"Yes, Muzan-sama." The male one muttered like a rebellious child talking to a parent he doesn't want to talk to.

"What are your names?"

"I am Gyuutarou and this is my sister Daki."

Resisting the urge to sigh, Muzan walked closer to the children. Close enough until his hands could reach them. Douma puts a hand on each of the sibling's shoulders, so that they didn't jump even though they are tense when Muzan touched each of their necks. With a stab of his thumb to their necks, a red crescent moon appeared on their skin. There, done.

"You will remain in the red light district of Edo." Muzan said, nonchalantly undo Daki's hair tie and combing them with his hands. "You both will be my ears and eyes of Edo. I trust you both know which are the important people. Avoid getting noticed or seen. You will listen to them, observe them, and report to me and Tamayo only. Understand?"

By the time he's finished, Daki's hair has formed a butterfly style ponytail. The girl looks bewildered but flustered when Muzan raised an eyebrow at her. Gyuutarou looks incredulous but yelped when Muzan reached to ruffle his hair.

"_Understand_?"

"Yes, Muzan-sama."

* * *

"Who is—" –_this sassy, lost child_? Muzan wanted to ask, but he didn't.

The child continued glaring at him, and Muzan continued staring at him, unimpressed.

"This is Yuushirou, my apprentice." Tamayo finally appeared from the hall of her new office, smiling as she puts a hand on Yuushirou's shoulder. "I heard from Douma that you like children, Muzan-sama. Isn't he cute?"

There's this _mirth_ on her face, and Yuushirou promptly turned his glare to this pleased expression and then twisted it _disgusted_ expression that would it not directed at him, Muzan would be impressed. As it is he's only impressed by how quick this kid's emotions changed and how he controlled his expression perfectly to cater to them. Must be hard, having emotions.

"Not if they bite." Muzan muttered lowly.

"What was that, Muzan-_kun_?"

Backtrack, _backtrack_. "Nothing, shishou." At least she's not alone, now. And Yuushirou behaves extremely well with Tamayo. She doesn't look like she's as sad she was when Muzan left, at least.

(_Yoriichi, after more than a hundred years, is still asleep. He couldn't help but started to think—maybe—no. No. He is stronger than that._)

* * *

What is it with his demons and bringing him children?

"… Is that kid for me?" Muzan asked, Tired, as he saw Akaza holding hands with a white-haired demon child trotting behind him.

Akaza beamed. "As expected of Muzan-sama! Yes, Muzan-sama, this is Rui. He was sickly, I found him with Douma's cult." Akaza's expression twisted to angry yet disgusted frown, "He was going to eat him."

_That's okay_. Muzan wanted to say, staring at nothing. _Rui can get eaten, Douma can eat children, I didn't say that you guys can't eat humans, just don't kill or eat the slayers_. _Akaza, why are you like this_?

While contemplating his choices on life (should he call Douma to eat this child? Should he let this child run free? _Why_ is Akaza bringing him here? What is he, a daycare?), Muzan felt a tug on his sleeve. Rui, white skinned, white haired, white kimono yet strangely red eyes, looked up at him. Muzan looked down, suddenly not knowing what to do in the face of the flat yet innocent expression of the child.

"Are you my father?" Rui asked.

….

He's not.

He's really not.

….

….

...

Damn it.

Shake your head, Muzan! Be strong!

Rui the child must interpret his jerking head as a nod and the demon child trotted happily beside him, climbing to his lap. Akaza beamed in sparkles. Rui beamed back, doubling the sparkles.

_What the fuck_, a part of Muzan's brain that are not dead by sparkles, whispered.

* * *

"Nakime, do I have a daycare of demon children?"

Muzan has asked it as a joke, seeing Yuushirou slowly crumbles in the face of the terrifyingly adorable menace with the flat expression called Rui. The child is dragging Yuushirou with his thread to play hide and seek with him. Yuushirou puts a formidable fight, yelling and screaming and a lot of curses as he digs his feet to the ground,but Rui is undeterred and his thread could cut stones. …Maybe it's Muzan's fault for the last one but moving on. Gyuutarou, from the tree where he perched at, are discreetly throwing rocks at Yuushirou and trying to ruin his balance, snickering.

Nakime is suspiciously silent beside him.

"Nakime?" He asked, glancing at her.

"Well." The demon said, a bit hesitantly. "About half of our forces are teenagers." Nakime said slowly, "And after that, forty percent are children. The remaining ten percent are adults."

….Huh.

"Didn't I say I want to be fair in demonizing people?" Not picking and all that? A few hundred years ago? Or more?

Nakime nodded, "Yes , Muzan-sama. But you always prioritize strays and children more. I think you did it unconsciously."

Well then. Hm.

"_GET YOUR FUCKING DOG OFF ME YOU USELESS DEMON LORD!" _

"Who." Muzan blinked, pretending not to see or hear the screaming boy in the garden. "Have you seen any demon lord, Nakime." He said, flatly.

"No, Muzan-sama." Nakime replied, just as dully and flatly.

"_YOU_—"

"Yuushirou!" Tamayo snapped from the kitchen, before Yuushirou could yell anymore. A faint girly giggling from Daki can be heard. "Language!"

"Bad language." Rui said, seriously yet flatly nodding while hand-chopping Yuushirou's back repeatedly, "Bad Yuushirou. Bad, _bad_."

Yuushirou screamed, for he is frustrated and he does not understand how a tiny gremlin like Rui can be stronger than him.

_Heh_. This isn't so bad, Muzan thinks.

* * *

"Muzan-sama! Look! I found a baby!"

"You—_WHAT_?!"

* * *

_A/N: Is the baby Inosuke? Yes, the baby is Inosuke._

_Me previous chapter: WE ARE ENTERING CANON!_  
_Also me now: haha Muzan daycare for demon children go brrr._

_Anyways thanks a lot for reading, reviewing, fav or follow. your support are always appreciated_


	4. Chapter 4

It's a human baby. _Thank God_ or whatever Deity out there that it's a _human_ baby. If it's demon baby then Muzan will have _an immortal baby_ in his hands, forever unable to become adult or able to learn languages; can you imagine a tiny thing who could fluently speaks like an adult? A tiny little bundle of meat who could walk and talk but _never_ grow? Or a tiny thing who could only cry and poop and needs to be fed eyeballs and blood every day? For eternity? Fuck no.

If Douma ever brings him a demon baby to him, Muzan is going to cut him to pieces, feed him to the crocodile, and eat Douma's skull himself.

The child is noisily, loudly, crying on his lab table, so Muzan quickly holds the baby in his hands, his doctor brain kicking his hands into gear to hold it properly. Rocking the baby covered in clothes in his hand gently to try calming it down. It did not work.

Douma, the little shit, is still smiling widely at Muzan.

"Douma."

"Yes, Muzan-sama?"

"If you ever bring me a baby again, you're going to be my permanent food source."

Muzan is not looking at Douma, but he knew Douma has stiffened, realizing the gravity of the situation. Afterall, despite being something akin to a King of Demons and respected (feared) as one, Muzan rarely ever threaten his 'children.' And when he has threats, he will see it _through_.

With a screaming baby in his hands and a decently Terrified™ Douma, Muzan jumped from his window and practically _flew_ to Tamayo's clinic.

* * *

Tamayo found Muzan in a messy operation room; sheets thrown about, closets and drawers open, bottles are out in the open. And a baby is on the bed, of course, screaming his lungs out like a baby he is.

"Shishou. I can explain." Muzan blurts out, before his brain could catch up.

Tamayo's smile turned even sharper than before. He narrowly dodged a syringe which Tamayo just threw at his _eye_. He hadn't even see the woman move. She's very _pissed_ and she's doing it while smiling angelically. As if she hadn't try poking his eye with a syringe filled with purple (wisteria) goo.

_Oh shit_.

"Sit down and start then, _Muzan-kun_."

* * *

Being a father is hard.

He doesn't really know how to start this. Being a normal father is, Muzan is sure hard enough. Now imagine you're a demon father with a lot of demon children under your wings, an immortal nemesis out there to chase and take down before he could take you down, and your baby is _human_.

See, his demon children are still self-sufficient. Sure his demons are mostly teenagers but even teenagers as young as Daki and Gyuutarou are running off on their own. Nakime's human years was fifteen and she does her own thing with her group of other demon teenagers harvesting human kidneys for art and vandalizing buildings with blood or whatnot. Like teenagers they are. Well, demon teenagers. But the point is they don't _need_ Muzan to be there. Even Rui, with his inhuman, terrifying obsession with concept of family, occasionally go off on his own.

Taking care of Hashibira Inosuke (written in the sheet where he is bundled in) is a challenge, but after some time, doable. Once Muzan realized what exactly he had to do and remember them in one of his brains perfectly, it's more than a little challenge. Not hard, per say, just a challenge.

Inosuke is a Loud baby when he cries, but he's quiet when he's full. After that he's usually busy trying to crawl from his crib or climbing a chair. He isn't picky on food, too. Instead he tried to eat _everything_. Spoon, his own clothes, plates, glass, anything laying around in his baby hands's reach. It's a bit tiring, but Muzan can generate extra eyes and limbs and coordinate them independently with his other brain to take care and look out for the child while he's doing something else, so, doable. Tamayo remarked that maybe he's teething, but far as Muzan remember Inosuke bites everything even since he was 3 months old. Inosuke is the one who made Muzan order a special leather-satin made gloves, just so the child could contently gnaw his fingers without accidentally turned to a demon. No Muzan uses it 24/7 because it's a hassle to take them off and use it again every hour or so.

Inosuke is one years old now, and he made it his mission to bite on everything his eyes can see. He can climb things too, so he tends to reach a lot of things with his tiny hands. Muzan is equal parts proud and incredulous, seeing Inosuke climb the table and then the cabinet up to the ceiling. It doesn't help that since Inosuke is never, ever alone, and there's always someone who talks to him almost every hour, he can already talk in one and three months old. Inosuke used his baby speech as a _weapon_ to get whatever he wants.

Muzan doesn't remember what was his first word, but remember the time Inosuke whines, "'too-shaaaa! up! up! too-shaa!" before Muzan's surprise of being called 'father' disappeared in Inosuke's whine to be picked up. Relenting, he picked the child up in his hands and Inosuke was instantly happy, circling his hands around Muzan's neck.

Daki _squeals_ to Inosuke's "'aghi! Aghi! Fwoa!" and instantly gave up her flower hair-pin to Inosuke to gnaw. She brought a lot of different blunt hair-pins for Inosuke to gnaw since then.

Gyuutarou puts up a formidable resistance while his sister is around but eventually gave up when Inosuke yells, "gwuuu'aaawooo!" and ever since become Inosuke's demon lift; Gyuutarou would lift Inosuke so high using his scarf the child would laugh-shriek in joy.

Nakime gave up stopping Inosuke from tangling his little body to her hair, instead continue reading him storybooks while Inosuke is busy using her hair as a blanket or a chewtoy. Sometimes her hair will end up with a lot of candies, sometimes just tangling to a horrible mess it's beyond saving. Muzan could see her teary eyes behind her hair, but she endures because it's Inosuke and he's _adorable_. Inosuke need only to smile and Nakime melts.

Akaza visited once and had then become Inosuke's horse—a very fast horse mind, Muzan would be concerned if it's any normal baby but it's Inosuke; the child screams in joy rather than in fear from the high speed Akaza went, carrying Inosuke on his shoulders and running around. Sometimes they laugh in sync, it's mildly terrifying.

Rui, who managed to visit once in the middle of the long term Mission Muzan has assigned him, smiles in joy seeing he has a little brother. They made a castle of white threads, covered by rocks, grass, candies, and Daki's flower hair pins in Tamayo's garden, which was very difficult to clean. None of them looks sorry in face of Tamayo's scolding, though.

Tamayo is Inosuke's personal doctor and aunt, and so Inosuke is terrified of her on bad days and obeys her without question on good days. In days in between, Inosuke would let himself sleep in her arms. Muzan understands; she's very calming and smells like flowers and herbs even without her blood demon art.

Today, Inosuke's biting crusade includes human fingers in a tube Inosuke insisted to open.

"No, Inosuke." Muzan said, a red, meaty tentacle which protruded out of Muzan's back grabbed the baby from the upper drawer, gently covering the child's figure, bringing Inosuke down. The child _yells_ when Muzan pried the tube from his hand.

"'Ooma eash!"

"Just because you saw Uncle Douma eat it doesn't mean you can eat it too."

Inosuke pouts. Muzan ignored that adorable pout out of practice and puts the child on his table, each eyeballs on his tentacle's eyes tracking down Inosuke's movement as it fenced around Inosuke loosely yet protectively.

Just as Muzan picked out a honey candy from the closet, Inosuke cried out, "'OOOMA-JIIII!"

Inosuke climbs out of Muzan's tentacle wall and jumped from the table. Douma, quick as he is, instantly materialized near the child to caught him. See, even Douma the empty doll couldn't resist Inosuke's charm. He lets the child climb his robes and to his shoulder, in perfect place to ruin Douma's blonde hair with his sticky fingers. The demon smiled the entire time, never speaking or making a noise. Knowing Douma, he's probably resisting himself not to say anything that Inosuke could copy, or wanting to kill Inosuke but refrained, or maybe he's just scared of Muzan if he ever hurt Inosuke. Either way, Douma makes a decent babysitter when he visits to eat leftover experiments.

The one who is immune or outright ignored Inosuke is Yuushirou. Muzan thinks the boy is terrified of Inosuke, and it's funny because his shifty and outright disappearance made Inosuke thinks Yuushirou is always playing magic hide and seek with him. Inosuke would trot around the house and clinic and squeals in joy every time he saw a hint of Yuushirou, running to catch the panicked and pissed off demon boy. And Inosuke's very, _very_ persistent. Yuushirou would be caught eventually. Muzan almost pity the boy. Almost.

* * *

Taking care of human children is also involving sunlight, typically by letting the child play under sunlight. They need it for their bones and growth development. Infant Inosuke enjoyed the sun on his being, two hours every day, as Muzan prepared a basket and a rope to pull Inosuke out of sunlight once he's done sunbathing. Sometimes he got only one hour because Inosuke is crying, or when he made a fuss, but most of the time he's sunbathing just fine. _Now_ though….

Now, Inosuke's caretakers are all demons here. The only one who could conquer the sun is still asleep, and Muzan realized that two years old Inosuke doesn't want to do anything with sunlight. He's very pale and he sleeps come sunlight, like a bat. No matter how everyone encouraged him to play outside with other children, once Inosuke is out in the sun and noticed no one follows him outside, he ran back home. He refused to come out again ever since.

Inosuke is four and Tamayo noticed his aversion to sunlight stunted his growth; despite his healthy food and his activeness, Inosuke is not very tall and he's rather thin. Muzan is apprehensive of it.

...

...

Desperate situation calls for desperate measures.

… That statement means involving Muzan putting a _lot_ of burn salve (he's using 3 bottles) on his entire body before he wrapped his hands in bandages, long yukata, a straw hat, a mask, and then an umbrella, before he braved himself to the sunlight. Only then, Inosuke finally want to play outside. Muzan expected himself to instantly combust the time he stepped to the sun, no matter his umbrella and his fully covered skin. But of course he doesn't. Yet, even with all this protection he uses, he could feel the sun heat stings his skin, like an annoying, under the skin pinpricks. It isn't painful, doesn't hurt him at all, but it's annoying and it feels like a death sentence breathing down on him. Like he's walking on tightrope with fire under him, ready to swallow once he sway.

"Come on tou-san! Faster! There're berries!"

"You can't eat them." Muzan said, automatic.

"But why?!"

"They're poisonous."

"But you and auntie are smarts and everyone can heal me right? _Right_?!"

"Inosuke." Muzan sighed, long-suffering and practiced.

The child shifted away from the bush of berries with a pout. "Fiiineeee… _OHO_?! Tou-san there! Did you see?!"

Inosuke is far too happy as he tugs Muzan's hand forward, asking things he's never seen before in the dark (butterflies, squirrels, berries, insects), so Muzan focused himself on the hyperactive child rather than his imminent death.

They traveled through the nearby forest, stopping in a cave where Muzan felt mildly safe while Inosuke's running around the clearing. With a note not to put anything in his mouth, Inosuke is apparently satisfied enough playing by himself; skipping rocks to nearby stream and picking flowers, asking Muzan what they are and if they are useful every once and then.

While keeping his ears out for Inosuke's faint voice in the distance, vaguely, Muzan heard growling. It came from the dark cave behind him. Confirming Inosuke is far from where he is and generating an extra eyeball in the back of his neck just in case, Muzan turned around.

It's a boar, emerging from the cave. A very big brown boar, actually. It dwarves Muzan, who sat down at the mouth of the cave to hid from the sunlight.

Muzan tips his hat up, just enough to show his red-slitted eyes; conveying how annoyed he is if this boar dare fought him and how he will _kill_ this boar to pieces if he dares—the boar _whimpers_ and took steps back. Animal instinct dictates that every animals are scared of him, the bigger predator, so it's good it's still working with a monstrous boar like this.

Inosuke appeared at the mouth of the cave then, bringing a lot of plants in his hands, no doubt about to ask Muzan about what they are. The child noticed the boar behind Muzan first though, and he _squealed_, abandoning the plants in his hands. With no ounce of fear and full on vibrating excitement in his tiny body, Inosuke runs to the boar and jumps to the fluffy thing. Muzan glared once more, and the wild animal cowered and finally sat down. Inosuke climbs it's snout and rubs his tiny hands on its fur, laughing.

* * *

"That's okay Tou-san."

"Hm?"

"You don't have to play with me anymore!" Tiny five years old Inosuke said, stomping imperiously and folding his hands in front of his chest as if saying 'duh, tou-san, keep up.' "I can play by myself! I'm strong!"

Muzan is not convinced of that. Not at all. Sure, Inosuke is strong and he's definitely smarter than most kids, having seen most tiny human children his age acts. But Inosuke is never alone since he's one. He gets lonely easily, despite his bravado.

"What brought this on?" Muzan asked instead.

Instead of answering, Inosuke pouts. His cheeks are stuffed with air it looks like an imitation of squirrel. An angry frown is on his face—his face is almost red in anger… no, embarrassment?

"Just stay here Tou-san!" Inosuke stomped once more before he jumped to the garden.

Taking a few steps, Inosuke stops, he turned around and glared at Muzan, daring him to follow. Muzan, unaffected, sit still on their porch, protected from sunlight, watching. This repeated at least five times until Inosuke reached the edge of the forest, disappearing behind the foliage.

Muzan counted three seconds before Inosuke's head pops out behind a tree, squinting and glaring at Muzan. As if he doesn't believe that Muzan wouldn't follow.

Finally satisfied, Inosuke nodded and runs to the forest. Muzan could hear Inosuke's footsteps cut through dry leaves and twigs, deeper and deeper through the trees.

.

.

.

.

... Inosuke's right, of course. However he's much too young to try to stop Muzan or detect him when he doesn't want to be seen; even in the light of day.

In the forest, Inosuke is wrestling the boar they had met a year ago; it has since become Inosuke's constant playmate. Settling down to a branch, leaning to a tree, Muzan shifted his position to get better protection from the shadows of the leaves and he kept quiet, watching the child play.

* * *

"TOU-SAN!"

Inosuke, ten years old, broke the door with his kick thunderously.

Douma is much too calm to choke on his food regardless of anything happened, but Muzan is not. He choked on his tea but managed to disguise it as a cough. In the other hall, Nakime tripped on her broom in surprise.

His eyebrows rose when he saw Inosuke holding two swords—definitely _nichirin_ blades in his hands.

"Inosuke-sama!" Akaza appeared from behind Inosuke, surprisingly bloodied and a bit haggard, "No!"

Too late, Inosuke set on a stance in the kitchen—Douma is curious but unmoving, as is Muzan. Too late, Muzan realized Inosuke's breathing pattern changed, before the child yelled, "BEAST BREATH TECHNIQUE! FIRT STYLE!"

It was only Douma's and Muzan's reflexes that allowed them to duck in time as Inosuke slashed the swords at the same time. Their whole kitchen is ruined, everything cut to two and an X cut formed on the wall behind him.

Impressive.

Muzan can guess what happened with Akaza and Inosuke in the forest when Muzan ordered Akaza to pick up Inosuke an hour ago. The sun has come down after all, Inosuke can get lost, nor matter how good his sight in the dark is. Instead, it seems like they met a demon and some slayers. Akaza is definitely poisoned, by his slightly labored breaths. And Inosuke managed to use breathing technique… just by seeing? Who knows that Inosuke is such a genius? Truly impressive.

But his kitchen is… _expensive_.

"Inosuke." Muzan said, materializing in front of the child and looming over his tiny figure like a big shadow. His voice was chilling low as Muzan glared down to the human child.

Inosuke gulped, _nichirin_ blades dropped from his trembling hands.

* * *

Muzan considered waking Yoriichi up.

After all, none in this house actually knows any proper training to use breathing technique. Inosuke could learn a lot from him. Yoriichi looks fine, too. It's been two hundred years already, how can he be asleep that long?

But when he contacted the slayer through his demon telepathy, his presence is… not there. Foggy. Even though Muzan is sitting beside his sleeping figure.

So, unfortunately, not yet.

* * *

Fortunately, all Demon Slayers write the same thing about their vague Breathing Technique training regime; _do it until you're half death, train yourself to death and back alive again_.

Muzan called it Run. Akaza called it Dodge the Demons.

Inosuke lovingly called it Hell while in tears.

Somewhere inside of Nakime's Interdimensional House, Inosuke screamed. Mad cackles followed. Probably Akaza and Gyuutarou. Muzan can't imagine Rui cackling, and anyways Rui isn't here, even though his thread traps are here.

A loud crash sounded. Hm. Muzan can guess Inosuke triggered another one of Rui's traps even from afar.

As Nakime blew her cup of tea in her hands, Muzan picks his cup up. Nursing the warm tea in his hands, he stared to the slightly moving rooms and ladders around him, expression serene.

"The tea is delicious today." He said.

A faint, terrorized, _DAAAAAAD! OTOU-SAN! AKAZA-JII IS FUCKING CRAZY! DAAAAAAAAAD! GET THE FUCK AWA—__**AAAAAAAAA**__,_ from afar could be heard.

"It is, Muzan-sama." Nakime replied, just as serene.

* * *

"Do you have everything?"

"Yep."

"Nichirin? Jacket? Hankerchief? Burn and wound salve? Wisteria vial?"

Wordlessly, boredly, fourteen years old Inosuke lifted every items asked from his pouch before he put them back carelessly. The boy is in his teenage rebelling stage, he's even more bratty than his six years old self. At least when he was six, he was cute.

Muzan tugged the purple scarf around Inosuke's neck tighter, sharply making him stumble. Asking the boy to focus. Inosuke yelped and glared, but ultimately looked down. Brat.

"Inosuke."

The boy's blue eyes looked up, stared at his red eyes.

… Now, what does he say?

He may be Inosuke's father for fourteen years now, but Muzan knows Inosuke is raised by everyone. His Demon Moons are co-parenting Inosuke, Tamayo filling in the blanks he couldn't fill because he doesn't understand human sometimes. A woman role he couldn't fulfill. His experience in parenting is still so.. insignificant, even though Inosuke does spend most of his time with Muzan than with any other demons.

"… I might not be your real father, but I'm proud of you." The demon decided to settle on, his voice was soft, almost a whisper. "No matter what happens, I will always be proud of you."

Inosuke puffed his cheeks behind his scarf. Before Muzan could confirm if those are tears in his blue eyes, the pre-teen hugged his father, burying his face on his suit. Gently, Muzan pats the child's head.

* * *

"They grew up so fast, aren't they?" Tamayo sighed from behind him, as soon as Inosuke's figure disappeared in the distance. "It feels like yesterday I was just changing his clothes and bathe him."

"You're just getting old, shishou." Muzan quipped.

"I don't want to hear it from such a sappy father like you, Muzan-kun." She cheerfully yet menacingly replied, "there there, you can cry on my bosom, my precious student."

What tears? Muzan grumbled softly.

"It's just dust."

The she-devil smiled serenely. "I'm sure they are."

"_Dust_."

* * *

Muzan turned around, walking back to Tamayo's clinic. He exhaled his breath softly.

… Now, if everything flows like he planned, then the end is near.

(_He will finally, finally, be able to rest_)

* * *

.

.

.

.

.

There was a smell. A particular smell.

It's different from the smell of the one who slaughtered his family though, but it held the same slight rotten smell, the same coppery tang of blood and filth. But this one is stronger, more _intense_. This isn't the one who turned Nezuko to demon, but this is definitely a demon smell.

As he pushed his feet forward to run faster and faster through the alley and the crowd, he's _scared_.

How can there be a demon amidst these many humans, in this kind of glimmering city? How _dare_ they hide and surround themselves by their victims like this? What kind horrible thing would he found at the center of this unbearably strong smell? Tanjirou moved faster, pushing a lot of people's body out of his way without apology. In the back of his mind, Tanjirou apologizes to everyone and then to his mother for his appalling manners.

It felt like forever, but finally he reached the center of the smell—the _demon_.

Tanjirou grabbed the man's wrist, holding back his fearful gasp as said demon turned to look at him. Ruby, red cat-like eyes of annoyed frown; smooth, pale face hooded by white hat; twin curly fringes framing the demon's annoyed sneer.

For a second Tanjirou was in panic because he might be facing a powerful demon in the middle of these crowds; alone, and Nezuko is not with him. For a second he felt his hairs stand on end with the demon's chilling glare, frozen in the demon's murderous intention. Tanjirou jerks stiffly to grab his sword and readies himself to face pain, but…

The demon's eyes looked at his earrings then. And suddenly Tanjirou could smell myriads of emotion, strong enough by their proximity, coming from this demon; _shock, surprise, guilt, sadness, guilt, panic, guilt_—and as quickly as they come, they disappeared along with the sneer, replaced by a carefully cool expression on the demon's face. He lifted his hand and Tanjirou began to pull his sword (albeit half-heartedly due to earlier barrage of emotions, and he doesn't want to hurt anyone in this crowd) for a fight, but again, the demon surprised him by carefully, _gently_, touched his right earring. The demon's fingers are cold when they brushed Tanjirou's cheek, and his touch is impossibly gentle for a demon. Tanjirou couldn't help but to look at his expression and noted how the demon's ruby eyes was softer somehow, rubbing the hanafuda symbol between his thumb and index finger. As if testing if they are real.

Eventually, they locked eyes and Tanjirou squared his shoulders, tense for a fight. The demon's eyes are not murderous or hostile, very different from any demons Tanjirou has encountered. It was still the carefully, coolly flat expression but his eyes are _searching_. Tanjirou did not back down from those assessing ruby eyes and, he doesn't know what, but it seems like the demon has found what he wanted to find. The demon lets out a slow breath and leaned back, yet Tanjirou is still wary.

When he spoke, his voice is silky smooth and barely above a whisper, "You're coming with me."

Alarm bell rings in his head but Tanjirou was too slow, _far_ too slow. In one motion, the demon stole his _nichirin_ from its place and scooped him in his hands. Before he knew it, Tanjirou was holding on the unknown demon's neck for his dear life as they were launched to the skies.

"_Nezuko_!" Tanjirou yelled, not looking down as the demon jumped over houses and towers and _dear god they're flying!_— "GO BACK!" He doesn't know what was it he pulled from the demon, maybe his hair, maybe his ear, and the demon hissed and tightened his grip in what Tanjirou thinks is bone-breaking strength to his waist. Tanjirou was undeterred though, he pointed to the other reaction and pulled again whatever it is he gripped, "My sister is over there! _Go back_!"

Tanjirou smelt annoyance followed by a deep sigh, but the demon did turn to where Tanjirou pointed and spotted his sister, her box, with an angry ramen vendor (_sorry jiisan_) in no time. In another one smooth, unseen move, he threw some money, swing her wooden box to his shoulder, and then perched Nezuko in his left hand.

Nezuko met Tanjirou's eyes behind the demon's back, and she blinked innocently, tilting her head as they sailed through the air; the moon behind them. Tentatively, Tanjirou smiled. So even his sister trusted this demon (to not be alarmed of his presence or his close proximity), whoever it is, so maybe Tanjirou can trust him too.

* * *

They arrived in a garden, greeted by a grumpy young (demon) boy who smoothed his scowl to a sneer once he locked eyes with Demon-san's eyes. Demon-san puts Nezuko and Tanjirou down, and he stuttered a thank you, which was ignored by Demon-san.

The boy scowls again once he saw Tanjirou and his sister, and Tanjirou glared back as he shifted to cover Nezuko because _no one_ glared to his sister. Tanjirou somehow knew the boy wanted to say something—a lot of things maybe, insulting definitely, but Demon-san's eyebrow rose as if in expectation and the demon boy broke their glaring match first by stepping inside.

Demon-san simply sat on the tatami of the living room, in front of a wooden desk, and Tanjirou followed behind him, pulling Nezuko with him.

Not one who can stand silence for long, Tanjirou asked, "May I know where we are?"

Demon-san glanced to him, and he replied quietly, "This is Tamayo's clinic for humans and demons."

Humans and _demons_? Feeling brave, Tanjirou asked again, "Why are we here, Demon-san?"

Before the demon could answer, the demon boy cursed before he literally disappeared. Maybe he run, maybe he jumped. But Tanjirou watched with no small amount of incredulity as the demon boy earlier practically flew to the hall, and in his place, another boy appeared from another hall across.

"TOU-SAN! WHERE'D YUUSHIRO GO?!"

The boy is using a black demon slayer standard uniform, a midnight blue hakama with red flowers adorning the end of the fabric. Black hair pulled up in a ponytail, the ends of his hair turning blue on his back. Two jagged nichirin blades propped by bandages on his hip.

When the boy's blue eyes locked with Tanjirou's red, he spluttered.

"MONJIRO?!"

"INOSUKE?!"

"TOU-SAN!" Inosuke whirled to Demon-san. Now it's Tanjirou's turn to splutter. _Tou-san_, he said. _Tou-san?! Inosuke's father is a Demon?! What?! __How?!__ "_YOU DIDN'T TELL ME TONTARO IS VISITING!"

"MY NAME IS TANJIRO! TAN-JI-RO!"

Yeah. Ignore the fact that you're just kidnapped by a not-bloodthirsty demon, Tanjiro. Ignore the fact that the father of the guy who helped you in Demon Slayer Selection the other day is a demon. Don't let them cause you existential crisis or headache! Not now! Ignore everything and focus on the idiot's inability to remember your name!

The audacity of this pretty guy!

"Yeah, yeah." Inosuke waved dismissively. "Kentaro."

"Tanjiro! Repeat it with me Inosuke! Tan. Ji. Ro!"

"Montaro."

"No! Repeat after me first!"

.

.

.

.

(Forgotten by the bickering pre-teen demon slayers, toddler Nezuko crawled to Muzan's lap. The one crowned Demon King by everyone but himself simply picks the child up his lap and let her lean to his chest. Her pink eyes growing heavier and heavier and Muzan combed his fingers through the child's hair, gently, softly.

By the time Tamayo appeared to traumatize Inosuke and Yoriichi's successor—Tanjirou—for causing a ruckus in her clinic, Nezuko is fast asleep.)

* * *

_A/N:_

_Inosuke's logic about names is,_  
_Inosuke: are they going to stay in my life as long as Uncle Akaza or Uncle Douma?_  
_Inosuke: That's right, they don't. I don't see why i have to remember their names._

_Sobs im happy crying tears of joy finally we are entering canon._  
_Also if you noticed the chapter count, that's because i want to add Yoriichi's Interlude and Inosuke's interlude next. They're more like side story, but have elements of main story too, so i decided to put it here too._

_Anyways thanks for reading, reviews, favs and following everyone!_


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